OpenMP: Handle non-executable directives in intervening code [PR120180,PR122306]

OpenMP: Handle non-executable directives in intervening code [PR120180,PR122306]

OpenMP 6 permits non-executable directives in intervening code; this commit adds
support for a sensible subset, namely metadirectives, nothing, assume, and
'error at(compilation)'.
Also handle the special case where a metadirective can be resolved at parse time
to 'omp nothing'.
This fixes a build issue that affects 10 out 12 SPECaccel benchmarks.

Co-authored by: Tobias Burnus <tburnus@baylibre.com>

	PR c/120180
	PR fortran/122306

gcc/c/ChangeLog:

	* c-parser.cc (c_parser_pragma): Accept a subset of non-executable
	OpenMP directives in intervening code.
	(c_parser_omp_error): Reject 'error at(execution)' in intervening code.
	(c_parser_omp_metadirective): Return early if only one selector matches
	and it resolves to 'omp nothing'.

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_omp_metadirective): Return early if only one
	selector matches and it resolves to 'omp nothing'.
	(cp_parser_omp_error): Reject 'error at(execution)' in intervening code.
	(cp_parser_pragma): Accept a subset of non-executable OpenMP directives
	as intervening code.

gcc/fortran/ChangeLog:

	* gfortran.h (enum gfc_exec_op): Add EXEC_OMP_FIRST_OPENMP_EXEC and
	EXEC_OMP_LAST_OPENMP_EXEC.
	* openmp.cc (gfc_match_omp_context_selector): Remove static. Remove
	checks on score. Add cleanup. Remove checks on trait properties.
	(gfc_match_omp_context_selector_specification): Remove static. Adjust
	calls to gfc_match_omp_context_selector.
	(gfc_match_omp_declare_variant): Adjust call to
	gfc_match_omp_context_selector_specification.
	(match_omp_metadirective): Likewise.
	(icode_code_error_callback): Reject all statements except
	'assume' and 'metadirective'.
	(gfc_resolve_omp_context_selector): New function.
	(resolve_omp_metadirective): Skip metadirectives which context selectors
	can be statically resolved to false. Replace metadirective by its body
	if only 'nothing' remains.
	(gfc_resolve_omp_declare): Call gfc_resolve_omp_context_selector for
	each variant.

gcc/testsuite/ChangeLog:

	* c-c++-common/gomp/imperfect1.c: Adjust dg-error.
	* c-c++-common/gomp/imperfect4.c: Likewise.
	* c-c++-common/gomp/pr120180.c: Move to...
	* c-c++-common/gomp/pr120180-1.c: ...here. Remove dg-error.
	* g++.dg/gomp/attrs-imperfect1.C: Adjust dg-error.
	* g++.dg/gomp/attrs-imperfect4.C: Likewise.
	* gfortran.dg/gomp/declare-variant-2.f90: Adjust dg-error.
	* gfortran.dg/gomp/declare-variant-20.f90: Likewise.
	* c-c++-common/gomp/pr120180-2.c: New test.
	* g++.dg/gomp/pr120180-1.C: New test.
	* gfortran.dg/gomp/pr120180-1.f90: New test.
	* gfortran.dg/gomp/pr120180-2.f90: New test.
	* gfortran.dg/gomp/pr122306-1.f90: New file.
	* gfortran.dg/gomp/pr122306-2.f90: New file.