OpenMP: Fixes for omp critical + hint

gcc/c-family/ChangeLog:

	* c-omp.c (c_finish_omp_critical): Check for no name but
	nonzero hint provided.

gcc/c/ChangeLog:

	* c-parser.c (c_parser_omp_clause_hint): Require nonnegative hint clause.
	(c_parser_omp_critical): Permit hint(0) clause without named critical.
	(c_parser_omp_construct): Don't assert if error_mark_node is returned.

gcc/cp/ChangeLog:

	* parser.c (cp_parser_omp_clause_hint): Require nonnegative hint.
	(cp_parser_omp_critical): Permit hint(0) clause without named critical.
	* pt.c (tsubst_expr): Re-check the latter for templates.

gcc/fortran/ChangeLog:

	* openmp.c (gfc_match_omp_critical): Fix handling hints; permit
	hint clause without named critical.
	(resolve_omp_clauses): Require nonnegative constant integer
	for the hint clause.
	(gfc_resolve_omp_directive): Check for no name but
	nonzero value for hint clause.
	* parse.c (parse_omp_structured_block): Fix same-name check
	for critical.
	* trans-openmp.c (gfc_trans_omp_critical): Handle hint clause properly.

libgomp/ChangeLog:

	* omp_lib.f90.in: Add omp_sync_hint_* and omp_sync_hint_kind.
	* omp_lib.h.in: Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/gomp/critical-3.C: Add nameless critical with hint testcase.
	* c-c++-common/gomp/critical-hint-1.c: New test.
	* c-c++-common/gomp/critical-hint-2.c: New test.
	* gfortran.dg/gomp/critical-hint-1.f90: New test.
	* gfortran.dg/gomp/critical-hint-2.f90: New test.