Replace NO_IMPLICIT_EXTERN_C with SYSTEM_IMPLICIT_EXTERN_C.

	gcc/
	Replace NO_IMPLICIT_EXTERN_C with SYSTEM_IMPLICIT_EXTERN_C.
	* doc/cpp.texi: Update comment.
	* doc/tm.texi: Rebuilt.
	* doc/tm.texi.in (NO_IMPLICIT_EXTERN_C): Replace with ...
	(SYSTEM_IMPLICIT_EXTERN_C): ... this, opposite sense.
	* doc/extend.texi (Backwards Compatibility): Clarify it is system
	headers affected by extern "C".
	* system.h: Poison NO_IMPLICIT_EXTERN_C.
	* config/alpha/alpha.h, config/arm/uclinux-elf.h,
	config/bfin/elf.h, config/cris/cris.h, config/darwin.h,
	config/dragonfly.h, config/freebsd.h, config/gnu-user.h,
	config/i386/cygming.h, config/i386/djgpp.h, config/i386/nto.h,
	config/ia64/hpux.h, config/lm32/lm32.h, config/lm32/uclinux-elf.h,
	config/lynx.h, config/mips/elf.h, config/mmix/mmix.h,
	config/netbsd.h, config/pa/pa-hpux.h, config/powerpcspe/sysv4.h,
	config/riscv/elf.h, config/rs6000/sysv4.h, config/rtems.h,
	config/s390/tpf.h, config/sh/newlib.h, config/sol2.h,
	config/sparc/openbsd64.h, config/sparc/sp-elf.h,
	config/sparc/sp64-elf.h, config/spu/spu.h,
	config/stormy16/stormy16.h, config/v850/v850.h,
	config/visium/visium.h, config/vx-common.h, config/xtensa/elf.h: Don't
	define NO_IMPLICIT_EXTERN_C.
	* config/rs6000/aix.h: Set SYSTEM_IMPLICIT_EXTERN_C.

	gcc/c-family/
	* c-lex.c (fe_file_change): Check SYSTEM_IMPLICIT_EXTERN_C not
	NO_IMPLICIT_EXTERN_C.

	gcc/cp/
	* cp/decl.c (decls_match): Check SYSTEM_IMPLICIT_EXTERN_C not
	NO_IMPLICIT_EXTERN_C.
	* cp/parser.c (cp_parser_parameter_declaration_clause): Likewise.

From-SVN: r262437

36 files changed, 3 insertions, 117 deletions

diff --git a/gcc/config/alpha/alpha.h b/gcc/config/alpha/alpha.h
index 1d32385..6802ef3 100644
--- a/gcc/config/alpha/alpha.h
+++ b/gcc/config/alpha/alpha.h
@@ -922,7 +922,4 @@ extern long alpha_auto_offset;
 /* By default, turn on GDB extensions.  */
 #define DEFAULT_GDB_EXTENSIONS 1
 
-/* The system headers under Alpha systems are generally C++-aware.  */
-#define NO_IMPLICIT_EXTERN_C
-
 #define TARGET_SUPPORTS_WIDE_INT 1
diff --git a/gcc/config/arm/uclinux-elf.h b/gcc/config/arm/uclinux-elf.h
index 54879c7..f78f279 100644
--- a/gcc/config/arm/uclinux-elf.h
+++ b/gcc/config/arm/uclinux-elf.h
@@ -48,9 +48,6 @@
     }						\
   while (false)
 
-/* Do not assume anything about header files.  */
-#define NO_IMPLICIT_EXTERN_C
-
 /* The GNU C++ standard library requires that these macros be defined.  */
 #undef CPLUSPLUS_CPP_SPEC
 #define CPLUSPLUS_CPP_SPEC "-D_GNU_SOURCE %(cpp)"
diff --git a/gcc/config/bfin/elf.h b/gcc/config/bfin/elf.h
index d8b0f37..ae16050 100644
--- a/gcc/config/bfin/elf.h
+++ b/gcc/config/bfin/elf.h
@@ -70,5 +70,3 @@ asm (TEXT_SECTION_ASM_OP);
 #undef SUBTARGET_DRIVER_SELF_SPECS
 #define SUBTARGET_DRIVER_SELF_SPECS \
      "%{mfdpic:-msim} %{mid-shared-library:-msim}"
-
-#define NO_IMPLICIT_EXTERN_C
diff --git a/gcc/config/cris/cris.h b/gcc/config/cris/cris.h
index 84c9292..e15f3f6 100644
--- a/gcc/config/cris/cris.h
+++ b/gcc/config/cris/cris.h
@@ -1030,8 +1030,6 @@ enum cris_symbol_type
 
 #define FUNCTION_MODE QImode
 
-#define NO_IMPLICIT_EXTERN_C
-
 /*
  * Local variables:
  * eval: (c-set-style "gnu")
diff --git a/gcc/config/darwin.h b/gcc/config/darwin.h
index 16c3b60..591188a 100644
--- a/gcc/config/darwin.h
+++ b/gcc/config/darwin.h
@@ -43,9 +43,6 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #define DARWIN_X86 0
 #define DARWIN_PPC 0
 
-/* Don't assume anything about the header files.  */
-#define NO_IMPLICIT_EXTERN_C
-
 /* Suppress g++ attempt to link in the math library automatically. */
 #define MATH_LIBRARY ""
 
diff --git a/gcc/config/dragonfly.h b/gcc/config/dragonfly.h
index ec9d9e0..4f53d22 100644
--- a/gcc/config/dragonfly.h
+++ b/gcc/config/dragonfly.h
@@ -104,10 +104,6 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #undef  OBJECT_FORMAT_ELF
 #define OBJECT_FORMAT_ELF
 
-/* Don't assume anything about the header files.  */
-#undef  NO_IMPLICIT_EXTERN_C
-#define NO_IMPLICIT_EXTERN_C	1
-
 /* Follow DragonFly's standard headers (<machine/stdint.h>, etc...).  */
 
 #undef  WCHAR_TYPE
diff --git a/gcc/config/freebsd.h b/gcc/config/freebsd.h
index 0c8bd29..9463dea 100644
--- a/gcc/config/freebsd.h
+++ b/gcc/config/freebsd.h
@@ -68,10 +68,6 @@ along with GCC; see the file COPYING3.  If not see
 #undef  OBJECT_FORMAT_ELF
 #define OBJECT_FORMAT_ELF
 
-/* Don't assume anything about the header files.  */
-#undef  NO_IMPLICIT_EXTERN_C
-#define NO_IMPLICIT_EXTERN_C	1
-
 /* Follow FreeBSD's standard headers (<sys/_types.h> etc...).  */
 
 #undef  WCHAR_TYPE
diff --git a/gcc/config/gnu-user.h b/gcc/config/gnu-user.h
index cba3c0b..aff034d 100644
--- a/gcc/config/gnu-user.h
+++ b/gcc/config/gnu-user.h
@@ -26,9 +26,6 @@ a copy of the GCC Runtime Library Exception along with this program;
 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 <http://www.gnu.org/licenses/>.  */
 
-/* Don't assume anything about the header files.  */
-#define NO_IMPLICIT_EXTERN_C
-
 #undef ASM_APP_ON
 #define ASM_APP_ON "#APP\n"
 
diff --git a/gcc/config/i386/cygming.h b/gcc/config/i386/cygming.h
index 1d35885..80a0a37 100644
--- a/gcc/config/i386/cygming.h
+++ b/gcc/config/i386/cygming.h
@@ -378,9 +378,6 @@ do {						\
 #endif
 #endif
 
-/* Don't assume anything about the header files.  */
-#define NO_IMPLICIT_EXTERN_C
-
 #undef PROFILE_HOOK
 #define PROFILE_HOOK(LABEL)						\
   if (MAIN_NAME_P (DECL_NAME (current_function_decl)))			\
diff --git a/gcc/config/i386/djgpp.h b/gcc/config/i386/djgpp.h
index 42130ed..01774ce 100644
--- a/gcc/config/i386/djgpp.h
+++ b/gcc/config/i386/djgpp.h
@@ -23,9 +23,6 @@ along with GCC; see the file COPYING3.  If not see
 #undef PREFERRED_DEBUGGING_TYPE
 #define PREFERRED_DEBUGGING_TYPE DWARF2_DEBUG
 
-/* Don't assume anything about the header files.  */
-#define NO_IMPLICIT_EXTERN_C
-
 #undef BSS_SECTION_ASM_OP
 #define BSS_SECTION_ASM_OP "\t.section\t.bss"
 
diff --git a/gcc/config/i386/nto.h b/gcc/config/i386/nto.h
index 339b0d1..fbcc668 100644
--- a/gcc/config/i386/nto.h
+++ b/gcc/config/i386/nto.h
@@ -98,8 +98,6 @@ crti.o%s \
 #undef WCHAR_TYPE_SIZE
 #define WCHAR_TYPE_SIZE BITS_PER_WORD
 
-#define NO_IMPLICIT_EXTERN_C 1
-
 #define TARGET_POSIX_IO
 
 #undef DBX_REGISTER_NUMBER
diff --git a/gcc/config/ia64/hpux.h b/gcc/config/ia64/hpux.h
index 5c5cf7f..d50c6ab 100644
--- a/gcc/config/ia64/hpux.h
+++ b/gcc/config/ia64/hpux.h
@@ -185,9 +185,6 @@ do {								\
 
 #define FLOAT_LIB_COMPARE_RETURNS_BOOL(MODE, COMPARISON) ((MODE) == TFmode)
 
-/* HP-UX headers are C++-compatible.  */
-#define NO_IMPLICIT_EXTERN_C
-
 /* HP-UX uses PROFILE_HOOK instead of FUNCTION_PROFILER but we need a
    FUNCTION_PROFILER defined because its use is not ifdefed.  When using
    PROFILE_HOOK, the profile call comes after the prologue.  */
diff --git a/gcc/config/lm32/lm32.h b/gcc/config/lm32/lm32.h
index c1b69fa..2a4a275 100644
--- a/gcc/config/lm32/lm32.h
+++ b/gcc/config/lm32/lm32.h
@@ -516,8 +516,4 @@ do {                                                            \
 
 #define FUNCTION_MODE SImode
 
-#ifndef NO_IMPLICIT_EXTERN_C
-#define NO_IMPLICIT_EXTERN_C
-#endif
-
 #define STORE_FLAG_VALUE 1
diff --git a/gcc/config/lm32/uclinux-elf.h b/gcc/config/lm32/uclinux-elf.h
index f6413c4..cfaca37 100644
--- a/gcc/config/lm32/uclinux-elf.h
+++ b/gcc/config/lm32/uclinux-elf.h
@@ -21,10 +21,6 @@
 /* elfos.h should have already been included.  Now just override
    any conflicting definitions and add any extras.  */
 
-/* Do not assume anything about header files.  */
-#undef NO_IMPLICIT_EXTERN_C
-#define NO_IMPLICIT_EXTERN_C
-
 /* The GNU C++ standard library requires that these macros be defined.  */
 #undef CPLUSPLUS_CPP_SPEC
 #define CPLUSPLUS_CPP_SPEC "-D_GNU_SOURCE %(cpp)"
diff --git a/gcc/config/lynx.h b/gcc/config/lynx.h
index 50c6d07..e2f768b 100644
--- a/gcc/config/lynx.h
+++ b/gcc/config/lynx.h
@@ -165,12 +165,6 @@ along with GCC; see the file COPYING3.  If not see
 # define PREFERRED_DEBUGGING_TYPE DBX_DEBUG
 #endif
 
-/* We have C++ support in our system headers.  */
-
-#ifndef NO_IMPLICIT_EXTERN_C
-# define NO_IMPLICIT_EXTERN_C
-#endif
-
 #ifndef TARGET_POSIX_IO
 # define TARGET_POSIX_IO
 #endif
diff --git a/gcc/config/mips/elf.h b/gcc/config/mips/elf.h
index dab96a6..98d4f80 100644
--- a/gcc/config/mips/elf.h
+++ b/gcc/config/mips/elf.h
@@ -46,5 +46,3 @@ along with GCC; see the file COPYING3.  If not see
 
 #undef  ENDFILE_SPEC
 #define ENDFILE_SPEC "crtend%O%s crtn%O%s"
-
-#define NO_IMPLICIT_EXTERN_C 1
diff --git a/gcc/config/mmix/mmix.h b/gcc/config/mmix/mmix.h
index aa998c2..7b46afc 100644
--- a/gcc/config/mmix/mmix.h
+++ b/gcc/config/mmix/mmix.h
@@ -789,8 +789,6 @@ typedef struct { int regs; int lib; } CUMULATIVE_ARGS;
 
 #define FUNCTION_MODE QImode
 
-#define NO_IMPLICIT_EXTERN_C
-
 /* mmix-knuth-mmixware target has no support of C99 runtime */
 #undef TARGET_LIBC_HAS_FUNCTION
 #define TARGET_LIBC_HAS_FUNCTION no_c99_libc_has_function
diff --git a/gcc/config/netbsd.h b/gcc/config/netbsd.h
index 8f9d5d3..dfd7c30 100644
--- a/gcc/config/netbsd.h
+++ b/gcc/config/netbsd.h
@@ -149,10 +149,6 @@ along with GCC; see the file COPYING3.  If not see
 #undef TARGET_POSIX_IO
 #define TARGET_POSIX_IO
 
-/* Don't assume anything about the header files.  */
-#undef  NO_IMPLICIT_EXTERN_C
-#define NO_IMPLICIT_EXTERN_C    1
-
 /* Define some types that are the same on all NetBSD platforms,
    making them agree with <machine/ansi.h>.  */
 
diff --git a/gcc/config/pa/pa-hpux.h b/gcc/config/pa/pa-hpux.h
index 19a632b..496cfb8 100644
--- a/gcc/config/pa/pa-hpux.h
+++ b/gcc/config/pa/pa-hpux.h
@@ -102,10 +102,6 @@ along with GCC; see the file COPYING3.  If not see
   "%{mlinker-opt:-O} %{!shared:-u main} %{static:-a archive} %{g*:-a archive} %{shared:-b}"
 #endif
 
-/* hpux8 and later have C++ compatible include files, so do not
-   pretend they are `extern "C"'.  */
-#define NO_IMPLICIT_EXTERN_C
-
 /* hpux11 and earlier don't have fputc_unlocked, so we must inhibit the
    transformation of fputs_unlocked and fprintf_unlocked to fputc_unlocked.  */
 #define DONT_HAVE_FPUTC_UNLOCKED
diff --git a/gcc/config/powerpcspe/sysv4.h b/gcc/config/powerpcspe/sysv4.h
index 4f35274..756e9e5 100644
--- a/gcc/config/powerpcspe/sysv4.h
+++ b/gcc/config/powerpcspe/sysv4.h
@@ -23,10 +23,6 @@
    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    <http://www.gnu.org/licenses/>.  */
 
-/* Header files should be C++ aware in general.  */
-#undef  NO_IMPLICIT_EXTERN_C
-#define NO_IMPLICIT_EXTERN_C
-
 /* Yes!  We are ELF.  */
 #define	TARGET_OBJECT_FORMAT OBJECT_ELF
 
diff --git a/gcc/config/riscv/elf.h b/gcc/config/riscv/elf.h
index a8357bb..0a4686a 100644
--- a/gcc/config/riscv/elf.h
+++ b/gcc/config/riscv/elf.h
@@ -32,5 +32,3 @@ along with GCC; see the file COPYING3.  If not see
 
 #undef  ENDFILE_SPEC
 #define ENDFILE_SPEC "crtend%O%s"
-
-#define NO_IMPLICIT_EXTERN_C 1
diff --git a/gcc/config/rs6000/aix.h b/gcc/config/rs6000/aix.h
index 0a93163..2d585d8 100644
--- a/gcc/config/rs6000/aix.h
+++ b/gcc/config/rs6000/aix.h
@@ -23,6 +23,9 @@
 #undef  TARGET_AIX
 #define TARGET_AIX 1
 
+/* System headers are not C++-aware.  */
+#define SYSTEM_IMPLICIT_EXTERN_C 1
+
 /* Linux64.h wants to redefine TARGET_AIX based on -m64, but it can't be used
    in the #if conditional in options-default.h, so provide another macro.  */
 #undef  TARGET_AIX_OS
diff --git a/gcc/config/rs6000/sysv4.h b/gcc/config/rs6000/sysv4.h
index 6b709fb..0c67634 100644
--- a/gcc/config/rs6000/sysv4.h
+++ b/gcc/config/rs6000/sysv4.h
@@ -23,10 +23,6 @@
    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    <http://www.gnu.org/licenses/>.  */
 
-/* Header files should be C++ aware in general.  */
-#undef  NO_IMPLICIT_EXTERN_C
-#define NO_IMPLICIT_EXTERN_C
-
 /* Yes!  We are ELF.  */
 #define	TARGET_OBJECT_FORMAT OBJECT_ELF
 
diff --git a/gcc/config/rtems.h b/gcc/config/rtems.h
index af58eb1..9879d52 100644
--- a/gcc/config/rtems.h
+++ b/gcc/config/rtems.h
@@ -22,10 +22,6 @@
    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    <http://www.gnu.org/licenses/>.  */
 
-/* The system headers under RTEMS are C++-aware.  */
-#undef NO_IMPLICIT_EXTERN_C
-#define NO_IMPLICIT_EXTERN_C
-
 /*
  * Dummy start/end specification to let linker work as
  * needed by autoconf scripts using this compiler.
diff --git a/gcc/config/s390/tpf.h b/gcc/config/s390/tpf.h
index 96802c6..5871a6b 100644
--- a/gcc/config/s390/tpf.h
+++ b/gcc/config/s390/tpf.h
@@ -30,7 +30,6 @@ along with GCC; see the file COPYING3.  If not see
 #define ASM_APP_ON "#APP\n"
 #undef ASM_APP_OFF
 #define ASM_APP_OFF "#NO_APP\n"
-#define NO_IMPLICIT_EXTERN_C
 #define TARGET_POSIX_IO
 
 #undef  SIZE_TYPE
diff --git a/gcc/config/sh/newlib.h b/gcc/config/sh/newlib.h
index 4d3ff02..9884856 100644
--- a/gcc/config/sh/newlib.h
+++ b/gcc/config/sh/newlib.h
@@ -23,7 +23,3 @@ along with GCC; see the file COPYING3.  If not see
 
 #undef LIB_SPEC
 #define LIB_SPEC "-lc -lgloss"
-
-#undef  NO_IMPLICIT_EXTERN_C
-#define NO_IMPLICIT_EXTERN_C 1
-
diff --git a/gcc/config/sol2.h b/gcc/config/sol2.h
index bc4f63d..8b67e78 100644
--- a/gcc/config/sol2.h
+++ b/gcc/config/sol2.h
@@ -423,9 +423,6 @@ along with GCC; see the file COPYING3.  If not see
    produce the same format.  */
 #define NM_FLAGS "-png"
 
-/* The system headers under Solaris 2 are C++-aware since 2.0.  */
-#define NO_IMPLICIT_EXTERN_C
-
 #define STDC_0_IN_SYSTEM_HEADERS 1
 
 /* Support Solaris-specific format checking for cmn_err.  */
diff --git a/gcc/config/sparc/openbsd64.h b/gcc/config/sparc/openbsd64.h
index 653eee9..55880f8 100644
--- a/gcc/config/sparc/openbsd64.h
+++ b/gcc/config/sparc/openbsd64.h
@@ -41,9 +41,6 @@ along with GCC; see the file COPYING3.  If not see
     }						\
   while (0)
 
-/* Inherited from sp64-elf.  */
-#undef NO_IMPLICIT_EXTERN_C
-
 #undef ASM_SPEC
 #define ASM_SPEC "\
 -s %{" FPIE_OR_FPIC_SPEC ":-K PIC} \
diff --git a/gcc/config/sparc/sp-elf.h b/gcc/config/sparc/sp-elf.h
index 0ee607c..0c53332 100644
--- a/gcc/config/sparc/sp-elf.h
+++ b/gcc/config/sparc/sp-elf.h
@@ -18,9 +18,6 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
-/* Don't assume anything about the header files.  */
-#define NO_IMPLICIT_EXTERN_C
-
 /* It's safe to pass -s always, even if -g is not used.  */
 #undef ASM_SPEC
 #define ASM_SPEC \
diff --git a/gcc/config/sparc/sp64-elf.h b/gcc/config/sparc/sp64-elf.h
index 5414b2d..3af2af0 100644
--- a/gcc/config/sparc/sp64-elf.h
+++ b/gcc/config/sparc/sp64-elf.h
@@ -27,9 +27,6 @@ along with GCC; see the file COPYING3.  If not see
 #undef SPARC_DEFAULT_CMODEL
 #define SPARC_DEFAULT_CMODEL CM_EMBMEDANY
 
-/* Don't assume anything about the header files.  */
-#define NO_IMPLICIT_EXTERN_C
-
 #undef ASM_SPEC
 #define ASM_SPEC "\
 -s %{" FPIE_OR_FPIC_SPEC ":-K PIC} \
diff --git a/gcc/config/spu/spu.h b/gcc/config/spu/spu.h
index e846f1c..af73958 100644
--- a/gcc/config/spu/spu.h
+++ b/gcc/config/spu/spu.h
@@ -483,8 +483,6 @@ do {									\
 
 #define FUNCTION_MODE QImode
 
-#define NO_IMPLICIT_EXTERN_C 1
-
 
 /* Address spaces.  */
 #define ADDR_SPACE_EA	1
diff --git a/gcc/config/stormy16/stormy16.h b/gcc/config/stormy16/stormy16.h
index 4667d8d..8adc6be 100644
--- a/gcc/config/stormy16/stormy16.h
+++ b/gcc/config/stormy16/stormy16.h
@@ -476,5 +476,3 @@ enum reg_class
 #define Pmode HImode
 
 #define FUNCTION_MODE HImode
-
-#define NO_IMPLICIT_EXTERN_C
diff --git a/gcc/config/v850/v850.h b/gcc/config/v850/v850.h
index 04d226a..d3391a6 100644
--- a/gcc/config/v850/v850.h
+++ b/gcc/config/v850/v850.h
@@ -834,12 +834,6 @@ extern const char * GHS_current_section_names [(int) COUNT_OF_GHS_SECTION_KINDS]
 
 #define TARGET_ASM_INIT_SECTIONS v850_asm_init_sections
 
-/* Define this so that the cc1plus will not think that system header files
-   need an implicit 'extern "C" { ... }' assumed.  This breaks testing C++
-   in a build directory where the libstdc++ header files are found via a
-   -isystem <path-to-build-dir>.  */
-#define NO_IMPLICIT_EXTERN_C
-
 #define ADJUST_INSN_LENGTH(INSN, LENGTH) \
   ((LENGTH) = v850_adjust_insn_length ((INSN), (LENGTH)))
 
diff --git a/gcc/config/visium/visium.h b/gcc/config/visium/visium.h
index dac9a45..f1bd00f 100644
--- a/gcc/config/visium/visium.h
+++ b/gcc/config/visium/visium.h
@@ -1211,14 +1211,6 @@ do									\
    machines this should be `QImode'. */
 #define FUNCTION_MODE SImode
 
-/* `NO_IMPLICIT_EXTERN_C'
-
-   Define this macro if the system header files support C++ as well as
-   C.  This macro inhibits the usual method of using system header
-   files in C++, which is to pretend that the file's contents are
-   enclosed in `extern "C" {...}'. */
-#define NO_IMPLICIT_EXTERN_C
-
 /* Dividing the Output into Sections (Texts, Data, ...)
 
    An object file is divided into sections containing different types
diff --git a/gcc/config/vx-common.h b/gcc/config/vx-common.h
index f5c398e..d83cbfb 100644
--- a/gcc/config/vx-common.h
+++ b/gcc/config/vx-common.h
@@ -18,10 +18,6 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
-/* VxWorks headers are C++-aware.  */
-#undef  NO_IMPLICIT_EXTERN_C
-#define NO_IMPLICIT_EXTERN_C
-
 /* Most of these will probably be overridden by subsequent headers.  We
    undefine them here just in case, and define VXWORKS_ versions of each,
    to be used in port-specific vxworks.h.  */
diff --git a/gcc/config/xtensa/elf.h b/gcc/config/xtensa/elf.h
index a95d7b3..736fd2d 100644
--- a/gcc/config/xtensa/elf.h
+++ b/gcc/config/xtensa/elf.h
@@ -20,9 +20,6 @@ along with GCC; see the file COPYING3.  If not see
 
 #define TARGET_SECTION_TYPE_FLAGS xtensa_multibss_section_type_flags
 
-/* Don't assume anything about the header files.  */
-#define NO_IMPLICIT_EXTERN_C
-
 #undef ASM_APP_ON
 #define ASM_APP_ON "#APP\n"