libgomp: Fix up icv-6.c [PR106894]

libgomp: Fix up icv-6.c [PR106894]

The thing is,
make check
or
make check RUNTESTFLAGS="c.exp='icv-6.c' c++.exp='icv-6.c'"
in libgomp obj dir work fine, but
make -j32 -k check RUNTESTFLAGS="c.exp='icv-6.c' c++.exp='icv-6.c'"
fails.
The thing is that the testcase as written relies on OMP_NUM_THREADS not being
set in environment (as it takes priority over OMP_NUM_THREADS_ALL for the
host).
So, if either a user has OMP_NUM_THREADS=42 in the environment by himself, or
when doing make check with -jN, we trigger:
          if test $$num_cpus -gt 8 && test -z "$$OMP_NUM_THREADS"; then \
            OMP_NUM_THREADS=8; export OMP_NUM_THREADS; \
            echo @@@ libgomp OMP_NUM_THREADS adjusted to 8 because of parallel
make check and too many CPUs; \
          fi; \
in libgomp/testsuite/Makefile.am and so the test fails.

2022-09-12  Jakub Jelinek  <jakub@redhat.com>

	PR libgomp/106894
	* testsuite/libgomp.c-c++-common/icv-6.c: Include string.h.
	(main): Avoid tests for which corresponding non-_ALL suffixed variable
	is in the environment, or for OMP_NUM_TEAMS on the device
	OMP_NUM_TEAMS_DEV_?.