There's no point in using value '-3', and even though not directly related,
value '-1' does match 'GOMP_DEVICE_ICV'.

	libgomp/
	* config/accel/openacc.f90 (acc_device_current): Set to '-1'.
	* openacc.f90 (acc_device_current): Likewise.
	* openacc.h (acc_device_current): Likewise.
	* openacc_lib.h (acc_device_current): Likewise.