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/bfd/Makefile.in b/bfd/Makefile.in
index 83d6865..3c9ebf3 100644
--- a/bfd/Makefile.in
+++ b/bfd/Makefile.in
@@ -122,10 +122,12 @@ am__aclocal_m4_deps = $(top_srcdir)/../config/acx.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)/bfd.m4 $(top_srcdir)/warning.m4 \
@@ -399,6 +401,9 @@ PACKAGE_URL = @PACKAGE_URL@
 PACKAGE_VERSION = @PACKAGE_VERSION@
 PATH_SEPARATOR = @PATH_SEPARATOR@
 PKGVERSION = @PKGVERSION@
+PKG_CONFIG = @PKG_CONFIG@
+PKG_CONFIG_LIBDIR = @PKG_CONFIG_LIBDIR@
+PKG_CONFIG_PATH = @PKG_CONFIG_PATH@
 POSUB = @POSUB@
 RANLIB = @RANLIB@
 REPORT_BUGS_TEXI = @REPORT_BUGS_TEXI@
@@ -416,6 +421,8 @@ WARN_CFLAGS = @WARN_CFLAGS@
 WARN_CFLAGS_FOR_BUILD = @WARN_CFLAGS_FOR_BUILD@
 WARN_WRITE_STRINGS = @WARN_WRITE_STRINGS@
 XGETTEXT = @XGETTEXT@
+ZSTD_CFLAGS = @ZSTD_CFLAGS@
+ZSTD_LIBS = @ZSTD_LIBS@
 abs_builddir = @abs_builddir@
 abs_srcdir = @abs_srcdir@
 abs_top_builddir = @abs_top_builddir@
@@ -520,7 +527,7 @@ libbfd_la_LDFLAGS = $(am__append_1) -release `cat libtool-soversion` \
 # case both are empty.
 ZLIB = @zlibdir@ -lz
 ZLIBINC = @zlibinc@
-AM_CFLAGS = $(WARN_CFLAGS) $(ZLIBINC)
+AM_CFLAGS = $(WARN_CFLAGS) $(ZLIBINC) $(ZSTD_CFLAGS)
 AM_CPPFLAGS = -DBINDIR='"$(bindir)"' -DLIBDIR='"$(libdir)"' \
 	@LARGEFILE_CPPFLAGS@ @HDEFINES@ @COREFLAG@ @TDEFINES@ \
 	$(CSEARCH) $(CSWITCHES) $(HAVEVECS) @INCINTL@
@@ -1199,7 +1206,7 @@ OFILES = $(BFD_BACKENDS) $(BFD_MACHINES) @COREFILE@ @bfd64_libs@
 libbfd_la_SOURCES = $(BFD32_LIBS_CFILES)
 EXTRA_libbfd_la_SOURCES = $(CFILES)
 libbfd_la_DEPENDENCIES = $(OFILES) ofiles
-libbfd_la_LIBADD = `cat ofiles` @SHARED_LIBADD@ $(LIBDL) $(ZLIB)
+libbfd_la_LIBADD = `cat ofiles` @SHARED_LIBADD@ $(LIBDL) $(ZLIB) $(ZSTD_LIBS)
 
 # libtool will build .libs/libbfd.a.  We create libbfd.a in the build
 # directory so that we don't have to convert all the programs that use