[binutils-gdb] sim; testsuite: allow tests to set no output

[sergiodj+buildbot@redhat.com]

*** TEST RESULTS FOR COMMIT 744b9a190b9b5b83d83f43d35b6ab6d20f49af8f ***

Author: Mike Frysinger <vapier@gentoo.org>
Branch: master
Commit: 744b9a190b9b5b83d83f43d35b6ab6d20f49af8f

sim; testsuite: allow tests to set no output
If a test doesn't write anything at all to stdout, the current test
framework can't support that.  Even if you put a blank output line:
	# output:
the setup happily clobbers that with a default pass/fail string.

Tweak the parsing logic so we only set the output to pass/fail when
the test has no output marker.