For libgomp OpenACC entry points, redefine the "device" argument to "flags"

... so that we're then able to use this for other flags in addition to
"GOACC_FLAG_HOST_FALLBACK".

	gcc/
	* omp-expand.c (expand_omp_target): Restructure OpenACC vs. OpenMP
	code paths.  Update for libgomp OpenACC entry points change.
	include/
	* gomp-constants.h (GOACC_FLAG_HOST_FALLBACK)
	(GOACC_FLAGS_MARSHAL_OP, GOACC_FLAGS_UNMARSHAL): Define.
	libgomp/
	* oacc-parallel.c (GOACC_parallel_keyed, GOACC_parallel)
	(GOACC_data_start, GOACC_enter_exit_data, GOACC_update)
	(GOACC_declare): Redefine the "device" argument to "flags".

From-SVN: r267448