OpenMP: Support OpenMP 5.0 "declare mapper" directives for C

OpenMP: Support OpenMP 5.0 "declare mapper" directives for C

This patch adds support for "declare mapper" directives (and the "mapper"
modifier on "map" clauses) for C.

gcc/c/ChangeLog:

	* c-decl.cc (c_omp_mapper_id, c_omp_mapper_decl, c_omp_mapper_lookup,
	c_omp_extract_mapper_directive, c_omp_map_array_section,
	c_omp_scan_mapper_bindings_r, c_omp_scan_mapper_bindings): New
	functions.
	* c-objc-common.h (LANG_HOOKS_OMP_FINISH_MAPPER_CLAUSES,
	LANG_HOOKS_OMP_MAPPER_LOOKUP, LANG_HOOKS_OMP_EXTRACT_MAPPER_DIRECTIVE,
	LANG_HOOKS_OMP_MAP_ARRAY_SECTION): Define langhooks for C.
	* c-parser.cc (c_parser_omp_clause_map): Add declare_mapper_p
	parameter; handle mapper modifier.
	(c_parser_omp_all_clauses): Update call to c_parser_omp_clause_map.
	(c_parser_omp_target): Instantiate explicit mappers and record bindings
	for implicit mappers.
	(c_parser_omp_declare_mapper): Parse "declare mapper" directives.
	(c_parser_omp_declare): Support "declare mapper".
	(c_parser_omp_declare_reduction): Use inform not error_at.
	* c-tree.h (c_omp_finish_mapper_clauses, c_omp_mapper_lookup,
	c_omp_extract_mapper_directive, c_omp_map_array_section,
	c_omp_mapper_id, c_omp_mapper_decl, c_omp_scan_mapper_bindings,
	c_omp_instantiate_mappers): Add prototypes.
	* c-typeck.cc (c_finish_omp_clauses): Handle GOMP_MAP_PUSH_MAPPER_NAME
	and GOMP_MAP_POP_MAPPER_NAME.
	(c_omp_finish_mapper_clauses): New function (langhook).

libgomp/ChangeLog:

	* testsuite/libgomp.c-c++-common/declare-mapper-9.c: Enable for C.
	* testsuite/libgomp.c-c++-common/declare-mapper-10.c: Likewise.
	* testsuite/libgomp.c-c++-common/declare-mapper-11.c: Likewise.
	* testsuite/libgomp.c-c++-common/declare-mapper-12.c: Likewise.
	* testsuite/libgomp.c-c++-common/declare-mapper-13.c: Likewise.
	* testsuite/libgomp.c-c++-common/declare-mapper-14.c: Likewise.

gcc/testsuite/ChangeLog:

	* c-c++-common/gomp/declare-mapper-3.c: Enable for C.
	* c-c++-common/gomp/declare-mapper-4.c: Likewise.
	* c-c++-common/gomp/declare-mapper-5.c: Likewise.
	* c-c++-common/gomp/declare-mapper-6.c: Likewise.
	* c-c++-common/gomp/declare-mapper-7.c: Likewise.
	* c-c++-common/gomp/declare-mapper-8.c: Likewise.
	* c-c++-common/gomp/declare-mapper-9.c: Likewise.
	* c-c++-common/gomp/declare-mapper-10.c: Likewise.
	* c-c++-common/gomp/declare-mapper-12.c: Likewise.
	* c-c++-common/gomp/map-6.c: Update dg-error.
	* gcc.dg/gomp/udr-3.c: Update for change to dg-note.
	* c-c++-common/gomp/declare-mapper-11.c: New.
	* gcc.dg/gomp/declare-mapper-10.c: New test.
	* gcc.dg/gomp/declare-mapper-11.c: New test.
	* gcc.dg/gomp/declare-mapper-13.c: New test.