openmp: Fix up handling of implicit lastprivate on outer constructs for...

openmp: Fix up handling of implicit lastprivate on outer constructs for implicit linear and lastprivate IVs [PR99928]

This patch fixes the handling of lastprivate propagation to outer combined/composite
leaf constructs from implicit linear or lastprivate clauses on simd IVs and adds missing
testsuite coverage for explicit and implicit lastprivate on simd IVs.

2021-05-21  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/99928
	* gimplify.c (omp_lastprivate_for_combined_outer_constructs): New
	function.
	(gimplify_scan_omp_clauses) <case OMP_CLAUSE_LASTPRIVATE>: Use it.
	(gimplify_omp_for): Likewise.

	* c-c++-common/gomp/pr99928-6.c: Remove all xfails.
	* c-c++-common/gomp/pr99928-13.c: New test.
	* c-c++-common/gomp/pr99928-14.c: New test.