Enhance 'libgomp.c-c++-common/requires-4.c', 'libgomp.c-c++-common/requires-5.c'...

Enhance 'libgomp.c-c++-common/requires-4.c', 'libgomp.c-c++-common/requires-5.c' testing

These should compile and link and execute in all configurations; host-fallback
execution, which we may actually verify.

Follow-up to recent commit 683f11843974f0bdf42f79cdcbb0c2b43c7b81b0
"OpenMP: Move omp requires checks to libgomp".

	libgomp/
	* testsuite/libgomp.c-c++-common/requires-4.c: Enhance testing.
	* testsuite/libgomp.c-c++-common/requires-5.c: Likewise.

(cherry picked from commit 5647e2c3853cbd51a6536a84b8eb0eb3c210dfbf)