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

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