Use "oacc kernels" attribute for OpenACC kernels

Use "oacc kernels" attribute for OpenACC kernels

	gcc/
	* omp-expand.c (expand_omp_target) <GF_OMP_TARGET_KIND_OACC_KERNELS>:
	Set "oacc kernels" attribute.
	* omp-general.c (oacc_set_fn_attrib): Remove is_kernel formal
	parameter.  Adjust all users.
	(oacc_fn_attrib_kernels_p): Remove function.
	* omp-offload.c (execute_oacc_device_lower): Look for "oacc
	kernels" attribute instead of calling oacc_fn_attrib_kernels_p.
	* tree-ssa-loop.c (gate_oacc_kernels): Likewise.
	* tree-parloops.c (create_parallel_loop): If oacc_kernels_p,
	assert "oacc kernels" attribute is set.
	gcc/testsuite/
	* c-c++-common/goacc/classify-kernels-unparallelized.c: Adjust.
	* c-c++-common/goacc/classify-kernels.c: Likewise.
	* c-c++-common/goacc/classify-parallel.c: Likewise.
	* c-c++-common/goacc/classify-routine.c: Likewise.
	* gfortran.dg/goacc/classify-kernels-unparallelized.f95: Likewise.
	* gfortran.dg/goacc/classify-kernels.f95: Likewise.
	* gfortran.dg/goacc/classify-parallel.f95: Likewise.
	* gfortran.dg/goacc/classify-routine.f95: Likewise.

From-SVN: r247955