OpenMP: Add early C/C++ parser support for 'groupprivate' directive

OpenMP: Add early C/C++ parser support for 'groupprivate' directive

After parsing the directive, 'sorry, unimplemented' is printed.
Note that restriction checks still have to be implemented, but this
depends on parser support for the 'local' clause of 'omp declare target',
which still has to be implemented.

gcc/c-family/ChangeLog:

	* c-omp.cc (c_omp_directives): Uncomment 'groupprivate'.
	* c-pragma.cc (omp_pragmas): Add PRAGMA_OMP_GROUPPRIVATE.
	* c-pragma.h (enum pragma_kind): Likewise.

gcc/c/ChangeLog:

	* c-parser.cc (OMP_GROUPPRIVATE_CLAUSE_MASK,
	c_parser_omp_groupprivate): New.
	(c_parser_pragma): Call it.
	(c_maybe_parse_omp_decl): Uncomment PRAGMA_OMP_GROUPPRIVATE
	check.

gcc/cp/ChangeLog:

	* parser.cc (OMP_GROUPPRIVATE_CLAUSE_MASK,
	cp_parser_omp_groupprivate): New.
	(cp_parser_pragma): Call it.
	(cp_maybe_parse_omp_decl): Uncomment PRAGMA_OMP_GROUPPRIVATE
	check.

gcc/testsuite/ChangeLog:

	* c-c++-common/gomp/groupprivate-1.c: New test.