libstdc++: Compare match_results for failed regex_match

libstdc++: Compare match_results for failed regex_match

The regex_match_debug testsuite helper doesn't compare the
std::match_results objects after a failed match, but it should do. The
standard says that the effects of a failed match on the match-results
are unspecified, except that [conditions testable by operator==]. So we
can check that the two sets of results compare equal even if the match
failed.

libstdc++-v3/ChangeLog:

	* testsuite/util/testsuite_regex.h (regex_match_debug): Compare
	results even if the match failed.