Make default compression gABI compliant

Make default compression gABI compliant

All programs in binutils+gdb git repo now support gABI compression
with the SHF_COMPRESSED bit.  This patch makes the zlib-gabi option
as compression default for gas, gold, ld and objcopy, instead of the
zlib-gnu option whose outputs are incompatible with gABI.

binutils/

	* objcopy.c (copy_file): Set BFD_COMPRESS_GABI if not
	zlib-gnu.
	* doc/binutils.texi: Change --compress-debug-sections and
	--compress-debug-sections=zlib to zlib-gabi.

binutils/testsuite/

	* binutils-all/compress.exp: Update.

gas/

	* as.c (parse_args): Make --compress-debug-sections and
	--compress-debug-sections=zlib the same as
	--compress-debug-sections=zlib-gabi.
	* doc/as.texinfo: Change --compress-debug-sections and
	--compress-debug-sections=zlib to zlib-gabi.

gold/

	* compressed_output.cc (Output_compressed_section::set_final_data_size):
	Make --compress-debug-sections=zlib the same as
	--compress-debug-sections=zlib-gabi.
	* testsuite/Makefile.am (flagstest_compress_debug_sections.check):
	Expect ".debug_.*" with the SHF_COMPRESSED bit, instead of
	".zdebug_".
	* testsuite/Makefile.in: Regenerated.

ld/

	* emultempl/elf32.em (gld${EMULATION_NAME}_handle_option): Make
	--compress-debug-sections=zlib the same as
	--compress-debug-sections=zlib-gabi.
	* ld.texinfo: Change --compress-debug-sections=zlib to zlib-gabi.

ld/testsuite/

	* ld-elf/zlibbegin.rS: Updated to .debug_.* with the
	SHF_COMPRESSED bit.
	* ld-elf/zlibnormal.rS: Likewise.