openmp: Add testsuite coverage for omp_{get_max,set_num}_threads and omp_{s,g}et_teams_thread_limit

This adds (C/C++ only) testsuite coverage for these new OpenMP 5.1 APIs.

2021-10-12  Jakub Jelinek  <jakub@redhat.com>

	* testsuite/libgomp.c-c++-common/icv-3.c: New test.
	* testsuite/libgomp.c-c++-common/icv-4.c: New test.