libstdc++: Add separate autoconf macro for std::float_t and std::double_t [PR109818]

This should make it possible to use openlibm with djgpp (and other
targets with missing C99 <math.h> functions). The <math.h> from openlibm
provides all the functions, but not the float_t and double_t typedefs.
By separating the autoconf checks for the functionsand the typedefs, we
don't disable support for all the functions just because those typedefs
are not present.

libstdc++-v3/ChangeLog:

	PR libstdc++/109818
	* acinclude.m4 (GLIBCXX_ENABLE_C99): Add separate check for
	float_t and double_t and define HAVE_C99_FLT_EVAL_TYPES.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* include/c_global/cmath (float_t, double_t): Guard using new
	_GLIBCXX_HAVE_C99_FLT_EVAL_TYPES macro.

4 files changed, 62 insertions, 6 deletions

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 6619407..6ae141b 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -1273,13 +1273,28 @@ AC_DEFUN([GLIBCXX_ENABLE_C99], [
         in <cmath> in namespace std for C++11.])
     fi
 
-    # Check for the existence of <math.h> functions.
-    AC_CACHE_CHECK([for ISO C99 function support for C++11 in <math.h>],
-    glibcxx_cv_c99_math_funcs, [
+    # Check for the existence of <math.h> typedefs.
+    AC_CACHE_CHECK([for ISO C99 float types for C++11 in <math.h>],
+    glibcxx_cv_c99_flt_eval_types, [
     AC_TRY_COMPILE([#include <math.h>],
 		   [// Types
 		    typedef double_t  my_double_t;
 		    typedef float_t   my_float_t;
+		   ],
+		   [glibcxx_cv_c99_flt_eval_types=yes],
+		   [glibcxx_cv_c99_flt_eval_types=no])
+    ])
+    if test x"$glibcxx_cv_c99_flt_eval_types" = x"yes"; then
+      AC_DEFINE(HAVE_C99_FLT_EVAL_TYPES, 1,
+		[Define if C99 float_t and double_t in <math.h> should be
+		imported in <cmath> in namespace std for C++11.])
+    fi
+
+    # Check for the existence of <math.h> functions.
+    AC_CACHE_CHECK([for ISO C99 function support for C++11 in <math.h>],
+    glibcxx_cv_c99_math_funcs, [
+    AC_TRY_COMPILE([#include <math.h>],
+		   [
 		    // Hyperbolic
 		    acosh(0.0);
 		    acoshf(0.0f);
diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in
index 4fbf5ef..5a95853 100644
--- a/libstdc++-v3/config.h.in
+++ b/libstdc++-v3/config.h.in
@@ -42,6 +42,10 @@
 /* Define to 1 if you have the `at_quick_exit' function. */
 #undef HAVE_AT_QUICK_EXIT
 
+/* Define if C99 float_t and double_t in <math.h> should be imported in
+   <cmath> in namespace std for C++11. */
+#undef HAVE_C99_FLT_EVAL_TYPES
+
 /* Define to 1 if the target assembler supports thread-local storage. */
 #undef HAVE_CC_TLS
 
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index ba328a6..70d169c 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -18275,6 +18275,43 @@ $as_echo "#define _GLIBCXX11_USE_C99_MATH 1" >>confdefs.h
 
     fi
 
+    # Check for the existence of <math.h> typedefs.
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking for ISO C99 float types for C++11 in <math.h>" >&5
+$as_echo_n "checking for ISO C99 float types for C++11 in <math.h>... " >&6; }
+if ${glibcxx_cv_c99_flt_eval_types+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+
+    cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <math.h>
+int
+main ()
+{
+// Types
+		    typedef double_t  my_double_t;
+		    typedef float_t   my_float_t;
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  glibcxx_cv_c99_flt_eval_types=yes
+else
+  glibcxx_cv_c99_flt_eval_types=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_c99_flt_eval_types" >&5
+$as_echo "$glibcxx_cv_c99_flt_eval_types" >&6; }
+    if test x"$glibcxx_cv_c99_flt_eval_types" = x"yes"; then
+
+$as_echo "#define HAVE_C99_FLT_EVAL_TYPES 1" >>confdefs.h
+
+    fi
+
     # Check for the existence of <math.h> functions.
     { $as_echo "$as_me:${as_lineno-$LINENO}: checking for ISO C99 function support for C++11 in <math.h>" >&5
 $as_echo_n "checking for ISO C99 function support for C++11 in <math.h>... " >&6; }
@@ -18288,9 +18325,7 @@ else
 int
 main ()
 {
-// Types
-		    typedef double_t  my_double_t;
-		    typedef float_t   my_float_t;
+
 		    // Hyperbolic
 		    acosh(0.0);
 		    acoshf(0.0f);
diff --git a/libstdc++-v3/include/c_global/cmath b/libstdc++-v3/include/c_global/cmath
index c80ee7c..b0ba395e 100644
--- a/libstdc++-v3/include/c_global/cmath
+++ b/libstdc++-v3/include/c_global/cmath
@@ -1877,9 +1877,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #undef truncf
 #undef truncl
 
+#ifdef _GLIBCXX_HAVE_C99_FLT_EVAL_TYPES
   // types
   using ::double_t;
   using ::float_t;
+#endif
 
   // functions
   using ::acosh;