Support multiple OpenACC wait clauses

Support multiple OpenACC wait clauses

Support for this is not explicitly called for in OpenACC 2.6, but given that
GCC internally decomposes "wait (1, 2)" into "wait (1) wait (2)" (similar for
other clauses, too), it's reasonable to also support that syntax in the front
ends -- which happens to already be the case for C, C++, and easy enough to do
for Fortran.

	gcc/fortran/
	* openmp.c (gfc_match_omp_clauses): Support multiple OpenACC wait
	clauses.
	gcc/testsuite/
	* c-c++-common/goacc/asyncwait-5.c: New file.
	* gfortran.dg/goacc/asyncwait-5.f: Likewise.

From-SVN: r266684