openmp: Fix ICE when splitting invalid depend(source)/depend(sink:vec)

openmp: Fix ICE when splitting invalid depend(source)/depend(sink:vec)

As we now create OMP_CLAUSE_DOACROSS rather than OMP_CLAUSE_DEPEND when
depend is used with source/sink modifiers, c_omp_split_clauses can see
OMP_CLAUSE_DOACROSS clause too before we diagnose it as erroneous.

The following patch treats it like OMP_CLAUSE_DEPEND during
the splitting but adds an assertion.

2022-09-06  Jakub Jelinek  <jakub@redhat.com>

	PR c/106836
	* c-omp.cc (c_omp_split_clauses): Handle OMP_CLAUSE_DOACROSS.

	* c-c++-common/gomp/pr106836.c: New test.

(cherry picked from commit 1bf8b7adc2de6f2ddaffa3af131b6855ae3e3793)