openmp: Regimplify operands of GIMPLE_COND in a few more places [PR103208]

As the testcase shows, the non-rectangular loop expansion code didn't
try to regimplify operands of GIMPLE_CONDs it built in some cases.
I have added a helper function which does that and used it in some places
that were regimplifying already to simplify those spots, plus added it
in a couple of other places where it was needed.

2021-11-16  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/103208
	* omp-expand.c (expand_omp_build_cond): New function.
	(expand_omp_for_init_counts, expand_omp_for_init_vars,
	expand_omp_for_static_nochunk, expand_omp_for_static_chunk): Use it.

	* c-c++-common/gomp/loop-11.c: New test.