OpenMP: Permit additional selector properties

OpenMP: Permit additional selector properties

This patch adds "hpe" to the known properties for the "vendor" selector,
and support for "acquire" and "release" for "atomic_default_mem_order".

gcc/ChangeLog
	* omp-general.cc (vendor_properties): Add "hpe".
	(atomic_default_mem_order_properties): Add "acquire" and "release".
	(omp_context_selector_matches): Handle "acquire" and "release".

gcc/testsuite/ChangeLog
	* c-c++-common/gomp/declare-variant-2.c: Don't expect error on
	"acquire" and "release".
	* gfortran.dg/gomp/declare-variant-2a.f90: Likewise.