openacc.h (enum acc_device_t): Reformat.

	gcc/
	* openacc.h (enum acc_device_t): Reformat. Ensure layout
	compatibility.
	(enum acc_async_t): Reformat.
	(acc_on_device): Declare compatible with builtin and provide C++
	wrapper.
	* testsuite/libgomp.oacc-c-c++-common/acc-on-device.c: New.

	gcc/testsuite/
	* c-c++-common/goacc/acc_on_device-2-off.c: Delete.
	* c-c++-common/goacc/acc_on_device-2.c: Delete.

From-SVN: r229562