PR23235, make check uses system installed ld

PR23235, make check uses system installed ld

This patch doesn't stop the build-id and debuglink tests using the
installed ld, it just prevents a compiler failure from resulting in a
test fail.  We could move the tests to the ld testsuite but it doesn't
seem all that important.

	PR 23235
	* testsuite/binutils-all/compress.exp (test_gnu_debuglink): Return
	unsupported rather than fail on compile errors.
	* testsuite/binutils-all/objdump.exp (test_build_id_debuglink):
	Likewise.  Save and restore CFLAGS_FOR_TARGET.