Improve diagnostic messages of "#pragma omp cancel", "#pragma omp cancellation point...

Improve diagnostic messages of "#pragma omp cancel", "#pragma omp cancellation point" parsing

	gcc/c/
	* c-parser.c (c_parser_pragma) <PRAGMA_OMP_CANCELLATION_POINT>:
	Move pragma context checking into...
	(c_parser_omp_cancellation_point): ... here, and improve
	diagnostic messages.
	* c-typeck.c (c_finish_omp_cancel)
	(c_finish_omp_cancellation_point): Improve diagnostic messages.
	gcc/cp/
	* parser.c (cp_parser_pragma) <PRAGMA_OMP_CANCELLATION_POINT>:
	Move pragma context checking into...
	(cp_parser_omp_cancellation_point): ... here, and improve
	diagnostic messages.
	* semantics.c (finish_omp_cancel, finish_omp_cancellation_point):
	Improve diagnostic messages.
	gcc/testsuite/
	* c-c++-common/gomp/cancel-1.c: Extend.

From-SVN: r237843