ld/testing: Fix error and warning checks in run_dump_test

ld/testing: Fix error and warning checks in run_dump_test

The options warning_output and error_output to the run_dump_test
function were incorrectly checking the return value from the regexp_diff
function, and so, as a result failing tests were showing as a pass.
Fixed in this commit.

ld/ChangeLog:

	* testsuite/lib/ld-lib.exp (run_dump_test): Fix check of return
	value from regexp_diff.
	* testsuite/ld-elf/orphan-5.l: Fix expected output.
	* testsuite/ld-elf/orphan-6.l: Likewise.