openmp: Fix handling of allocate clause on taskloop

openmp: Fix handling of allocate clause on taskloop

This patch fixes gimplification of allocate clause on taskloop - puts
allocate on inner taskloop only if there is allocate clause, because otherwise
the data sharing clauses are only on the task construct in the construct sandwich.

2020-10-30  Jakub Jelinek  <jakub@redhat.com>

	* gimplify.c (gimplify_scan_omp_clauses): Force
	OMP_CLAUSE_ALLOCATE_ALLOCATOR into a temporary if it is non-NULL and
	non-constant.
	(gimplify_omp_for): Only put allocate on inner taskloop if lastprivate
	for the same variable is going to be put there, and in that case
	if the OMP_CLAUSE_ALLOCATE_ALLOCATOR is non-NULL non-constant, make
	the allocator firstprivate on task.

	* c-c++-common/gomp/allocate-3.c: New test.