libgomp: Normalize the names of a few functions of the libgomp plugin API

libgomp: Normalize the names of a few functions of the libgomp plugin API

	libgomp/
	* libgomp-plugin.h (GOMP_OFFLOAD_openacc_parallel): Rename to
	GOMP_OFFLOAD_openacc_exec.  Adjust all users.
	(GOMP_OFFLOAD_openacc_get_current_cuda_device): Rename to
	GOMP_OFFLOAD_openacc_cuda_get_current_device.  Adjust all users.
	(GOMP_OFFLOAD_openacc_get_current_cuda_context): Rename to
	GOMP_OFFLOAD_openacc_cuda_get_current_context.  Adjust all users.
	(GOMP_OFFLOAD_openacc_get_cuda_stream): Rename to
	GOMP_OFFLOAD_openacc_cuda_get_stream.  Adjust all users.
	(GOMP_OFFLOAD_openacc_set_cuda_stream): Rename to
	GOMP_OFFLOAD_openacc_cuda_set_stream.  Adjust all users.

From-SVN: r245125