binutils, gdb: support zstd compressed debug sections

PR29397 PR29563: Add new configure option --with-zstd which defaults to
auto.  If pkgconfig/libzstd.pc is found, define HAVE_ZSTD and support
zstd compressed debug sections for most tools.

* bfd: for addr2line, objdump --dwarf, gdb, etc
* gas: support --compress-debug-sections=zstd
* ld: support ELFCOMPRESS_ZSTD input and --compress-debug-sections=zstd
* objcopy: support ELFCOMPRESS_ZSTD input for
  --decompress-debug-sections and --compress-debug-sections=zstd
* gdb: support ELFCOMPRESS_ZSTD input.  The bfd change references zstd
  symbols, so gdb has to link against -lzstd in this patch.

If zstd is not supported, ELFCOMPRESS_ZSTD input triggers an error.  We
can avoid HAVE_ZSTD if binutils-gdb imports zstd/ like zlib/, but this
is too heavyweight, so don't do it for now.

```
% ld/ld-new a.o
ld/ld-new: a.o: section .debug_abbrev is compressed with zstd, but BFD is not built with zstd support
...

% ld/ld-new a.o --compress-debug-sections=zstd
ld/ld-new: --compress-debug-sections=zstd: ld is not built with zstd support

% binutils/objcopy --compress-debug-sections=zstd a.o b.o
binutils/objcopy: --compress-debug-sections=zstd: binutils is not built with zstd support

% binutils/objcopy b.o --decompress-debug-sections
binutils/objcopy: zstd.o: section .debug_abbrev is compressed with zstd, but BFD is not built with zstd support
...
```

1 files changed, 10 insertions, 3 deletions

diff --git a/gas/Makefile.in b/gas/Makefile.in
index c57d78f..5a4dd70 100644
--- a/gas/Makefile.in
+++ b/gas/Makefile.in
@@ -140,10 +140,12 @@ am__aclocal_m4_deps = $(top_srcdir)/../bfd/acinclude.m4 \
 	$(top_srcdir)/../config/lead-dot.m4 \
 	$(top_srcdir)/../config/nls.m4 \
 	$(top_srcdir)/../config/override.m4 \
+	$(top_srcdir)/../config/pkg.m4 \
 	$(top_srcdir)/../config/plugins.m4 \
 	$(top_srcdir)/../config/po.m4 \
 	$(top_srcdir)/../config/progtest.m4 \
-	$(top_srcdir)/../config/zlib.m4 $(top_srcdir)/../libtool.m4 \
+	$(top_srcdir)/../config/zlib.m4 \
+	$(top_srcdir)/../config/zstd.m4 $(top_srcdir)/../libtool.m4 \
 	$(top_srcdir)/../ltoptions.m4 $(top_srcdir)/../ltsugar.m4 \
 	$(top_srcdir)/../ltversion.m4 $(top_srcdir)/../lt~obsolete.m4 \
 	$(top_srcdir)/acinclude.m4 $(top_srcdir)/../bfd/version.m4 \
@@ -429,6 +431,9 @@ PACKAGE_TARNAME = @PACKAGE_TARNAME@
 PACKAGE_URL = @PACKAGE_URL@
 PACKAGE_VERSION = @PACKAGE_VERSION@
 PATH_SEPARATOR = @PATH_SEPARATOR@
+PKG_CONFIG = @PKG_CONFIG@
+PKG_CONFIG_LIBDIR = @PKG_CONFIG_LIBDIR@
+PKG_CONFIG_PATH = @PKG_CONFIG_PATH@
 POSUB = @POSUB@
 RANLIB = @RANLIB@
 SED = @SED@
@@ -443,6 +448,8 @@ WARN_WRITE_STRINGS = @WARN_WRITE_STRINGS@
 XGETTEXT = @XGETTEXT@
 YACC = `if [ -f ../bison/bison ] ; then echo ../bison/bison -y -L../bison/bison ; else echo @YACC@ ; fi`
 YFLAGS = @YFLAGS@
+ZSTD_CFLAGS = @ZSTD_CFLAGS@
+ZSTD_LIBS = @ZSTD_LIBS@
 abs_builddir = @abs_builddir@
 abs_srcdir = @abs_srcdir@
 abs_top_builddir = @abs_top_builddir@
@@ -524,7 +531,7 @@ ZLIBINC = @zlibinc@
 # maintainer mode is disabled.  Avoid this.
 am__skiplex = 
 am__skipyacc = 
-AM_CFLAGS = $(WARN_CFLAGS) $(ZLIBINC)
+AM_CFLAGS = $(WARN_CFLAGS) $(ZLIBINC) $(ZSTD_CFLAGS)
 TARG_CPU = @target_cpu_type@
 TARG_CPU_C = $(srcdir)/config/tc-@target_cpu_type@.c
 TARG_CPU_O = config/tc-@target_cpu_type@.@OBJEXT@
@@ -874,7 +881,7 @@ GASLIBS = @OPCODES_LIB@ ../bfd/libbfd.la ../libiberty/libiberty.a
 STAGESTUFF = *.@OBJEXT@ $(noinst_PROGRAMS)
 as_new_SOURCES = $(GAS_CFILES)
 as_new_LDADD = $(TARG_CPU_O) $(OBJ_FORMAT_O) $(ATOF_TARG_O) \
-	$(extra_objects) $(GASLIBS) $(LIBINTL) $(LIBM) $(ZLIB)
+	$(extra_objects) $(GASLIBS) $(LIBINTL) $(LIBM) $(ZLIB) $(ZSTD_LIBS)
 
 as_new_DEPENDENCIES = $(TARG_CPU_O) $(OBJ_FORMAT_O) $(ATOF_TARG_O) \
 	$(extra_objects) $(GASLIBS) $(LIBINTL_DEP)