OpenACC 2.7: default clause support for data constructs

This patch implements the OpenACC 2.7 addition of default(none|present) support
for data constructs.

Now, specifying "default(none|present)" on a data construct turns on same
default clause behavior for all lexically enclosed compute constructs (which
don't already themselves have a default clause).

gcc/c/ChangeLog:
	* c-parser.cc (OACC_DATA_CLAUSE_MASK): Add PRAGMA_OACC_CLAUSE_DEFAULT.

gcc/cp/ChangeLog:
	* parser.cc (OACC_DATA_CLAUSE_MASK): Add PRAGMA_OACC_CLAUSE_DEFAULT.

gcc/fortran/ChangeLog:
	* openmp.cc (OACC_DATA_CLAUSES): Add OMP_CLAUSE_DEFAULT.

gcc/ChangeLog:
	* gimplify.cc (oacc_region_type_name): New function.
	(oacc_default_clause): If no 'default' clause appears on this
	compute construct, see if one appears on a lexically containing
	'data' construct.
	(gimplify_scan_omp_clauses): Upon OMP_CLAUSE_DEFAULT case, set
	ctx->oacc_default_clause_ctx to current context.

gcc/testsuite/ChangeLog:
	* c-c++-common/goacc/default-3.c: Adjust testcase.
	* c-c++-common/goacc/default-4.c: Adjust testcase.
	* c-c++-common/goacc/default-5.c: Adjust testcase.
	* gfortran.dg/goacc/default-3.f95: Adjust testcase.
	* gfortran.dg/goacc/default-4.f: Adjust testcase.
	* gfortran.dg/goacc/default-5.f: Adjust testcase.

Co-authored-by: Thomas Schwinge <thomas@codesourcery.com>