Enable gimplify GOMP_MAP_STRUCT handling of (COMPONENT_REF (INDIRECT_REF ...)) map...

Enable gimplify GOMP_MAP_STRUCT handling of (COMPONENT_REF (INDIRECT_REF ...)) map clauses.

This patch tries to allow map(A->ptr) to be properly handled the same way as
map(B.ptr) expressions. map(struct:*A) clauses are now produced during
gimplify.

This patch, as of time of commit, is only pushed to devel/omp/gcc-10, not yet
submitted as mainline patch to upstream.

2021-02-08  Chung-Lin Tang  <cltang@codesourcery.com>

gcc/ChangeLog:

	* gimplify.c ("tree-hash-traits.h"): Add include.
	(gimplify_scan_omp_clauses): Change struct_map_to_clause to type
	hash_map<tree_operand, tree> *. Adjust struct map handling to handle
	cases of *A and A->B expressions.
	(gimplify_adjust_omp_clauses): Move GOMP_MAP_STRUCT removal code for
	exit data directives code to earlier position.

gcc/testsuite/ChangeLog:

	* g++.dg/gomp/target-3.C: Adjust testcase gimple scanning.
	* g++.dg/gomp/target-this-2.C: Likewise.
	* g++.dg/gomp/target-this-3.C: Likewise.
	* g++.dg/gomp/target-this-4.C: Likewise.

libgomp/ChangeLog:

	* testsuite/libgomp.c++/target-23.C: New testcase.