xcoff dependency list for static libraries

xcoff dependency list for static libraries

This patch fixes fails adding library dependencies for xcoff, and
improves the error message should stat fail for an archive member.
"tmpdir/artest.a: File not found" is plainly wrong.

Fixes these fails:
powerpc-aix5.1  +FAIL: ar adding library dependencies
powerpc-aix5.2  +FAIL: ar adding library dependencies
rs6000-aix4.3.3  +FAIL: ar adding library dependencies
rs6000-aix5.1  +FAIL: ar adding library dependencies
rs6000-aix5.2  +FAIL: ar adding library dependencies

	* archive.c (bfd_ar_hdr_from_filesystem): Use bfd_set_input_error
	when stat of archive member fails.
	* coff-rs6000.c (xcoff_write_archive_contents_old),
	(xcoff_write_archive_contents_big): Likewise, and handle in-memory
	bfd.