OpenMP/Fortran: Permit end-clause on directive

gcc/fortran/ChangeLog:

	* openmp.cc (OMP_DO_CLAUSES, OMP_SCOPE_CLAUSES,
	OMP_SECTIONS_CLAUSES): Add 'nowait'.
	(OMP_SINGLE_CLAUSES): Add 'nowait' and 'copyprivate'.
	(gfc_match_omp_distribute_parallel_do,
	gfc_match_omp_distribute_parallel_do_simd,
	gfc_match_omp_parallel_do,
	gfc_match_omp_parallel_do_simd,
	gfc_match_omp_parallel_sections,
	gfc_match_omp_teams_distribute_parallel_do,
	gfc_match_omp_teams_distribute_parallel_do_simd): Disallow 'nowait'.
	(gfc_match_omp_workshare): Match 'nowait' clause.
	(gfc_match_omp_end_single): Use clause matcher for 'nowait'.
	(resolve_omp_clauses): Reject 'nowait' + 'copyprivate'.
	* parse.cc (decode_omp_directive): Break too long line.
	(parse_omp_do, parse_omp_structured_block): Diagnose duplicated
	'nowait' clause.

libgomp/ChangeLog:

	* libgomp.texi (OpenMP 5.2): Mark end-directive as Y.

gcc/testsuite/ChangeLog:

	* gfortran.dg/gomp/copyprivate-1.f90: New test.
	* gfortran.dg/gomp/copyprivate-2.f90: New test.
	* gfortran.dg/gomp/nowait-2.f90: Move dg-error tests ...
	* gfortran.dg/gomp/nowait-4.f90: ... to this new file.
	* gfortran.dg/gomp/nowait-5.f90: New test.
	* gfortran.dg/gomp/nowait-6.f90: New test.
	* gfortran.dg/gomp/nowait-7.f90: New test.
	* gfortran.dg/gomp/nowait-8.f90: New test.