aix: collect2 text files in archive

aix: collect2 text files in archive

Rust places text files in archives.  AIX ld ignores such files with a
warning.  The collect2 wrapper for ld had been exiting with a fatal
error if it scanned an archive that contained a non-COFF file.

This patch updates collect2.c to issue a warning and ignore the file
member, matching the behavior of AIX ld.  GCC can encounter archives
created by Rust and should not issue a fatal error.  This changes
fatal_error to warning, with an implicit location and no associated
optimization flag.

gcc/ChangeLog:

2021-05-20  Clement Chigot  <clement.chigot@atos.net>
	    David Edelsohn  <dje.gcc@gmail.com>

	* collect2.c (scan_prog_file): Issue non-fatal warning for
	non-COFF files.

(cherry picked from commit 5a3bf28119c7a8d2d43d26b5eee588ee0e4472e5)