Properly check --compress-debug-sections=XXX
We can't check if input is ELF in copy_file since some targets may only
set xvec after bfd_check_format_matches is called. This patch moves
this check to copy_object.
bfd/
* elfxx-target.h (TARGET_BIG_SYM): Add BFD_COMPRESS_GABI to
object_flags.
(TARGET_LITTLE_SYM): Likewise.
binutils/
* objcopy.c (do_debug_sections): Use bit patterns.
(copy_object): Return FALSE for compress_zlib, compress_gnu_zlib
and compress_gabi_zlib on non-ELF input.
(copy_file): Don't check non-ELF input here.