[binutils-gdb] Don't write the zlib header if not used

[sergiodj+buildbot@redhat.com]

*** TEST RESULTS FOR COMMIT 8d00121477371cfd1596118af062fe6ff4e263b7 ***

Author: H.J. Lu <hjl.tools@gmail.com>
Branch: master
Commit: 8d00121477371cfd1596118af062fe6ff4e263b7

Don't write the zlib header if not used
No need to write the zlib header if compression didn't make the section
smaller.

	PR binutils/18087
	* compress.c (bfd_compress_section_contents): Don't write the
	zlib header and set contents as well as compress_status if
	compression didn't make the section smaller.
	(bfd_init_section_compress_status): Don't check compression
	size here.