OpenMP: Add get_device_from_uid/omp_get_uid_from_device routines

Those TR13/OpenMP 6.0 routines permit a reproducible offloading to
a specific device by mapping an OpenMP device number to a
unique ID (UID). The GPU device UIDs should be universally unique,
the one for the host is not.

gcc/ChangeLog:

	* omp-general.cc (omp_runtime_api_procname): Add
	get_device_from_uid and omp_get_uid_from_device routines.

include/ChangeLog:

	* cuda/cuda.h (cuDeviceGetUuid): Declare.
	(cuDeviceGetUuid_v2): Add prototype.

libgomp/ChangeLog:

	* config/gcn/target.c (omp_get_uid_from_device,
	omp_get_device_from_uid): Add stub implementation.
	* config/nvptx/target.c (omp_get_uid_from_device,
	omp_get_device_from_uid): Likewise.
	* fortran.c (omp_get_uid_from_device_,
	omp_get_uid_from_device_8_): New functions.
	* libgomp-plugin.h (GOMP_OFFLOAD_get_uid): Add prototype.
	* libgomp.h (struct gomp_device_descr): Add 'uid' and 'get_uid_func'.
	* libgomp.map (GOMP_6.0): New, includind the new UID routines.
	* libgomp.texi (OpenMP Technical Report 13): Mark UID routines as 'Y'.
	(Device Information Routines): Document new UID routines.
	(Offload-Target Specifics): Document UID format.
	* omp.h.in (omp_get_device_from_uid, omp_get_uid_from_device):
	New prototype.
	* omp_lib.f90.in (omp_get_device_from_uid, omp_get_uid_from_device):
	New interface.
	* omp_lib.h.in: Likewise.
	* plugin/cuda-lib.def: Add cuDeviceGetUuid and cuDeviceGetUuid_v2 via
	CUDA_ONE_CALL_MAYBE_NULL.
	* plugin/plugin-gcn.c (GOMP_OFFLOAD_get_uid): New.
	* plugin/plugin-nvptx.c (GOMP_OFFLOAD_get_uid): New.
	* target.c (str_omp_initial_device): New static var.
	(STR_OMP_DEV_PREFIX): Define.
	(gomp_get_uid_for_device, omp_get_uid_from_device,
	omp_get_device_from_uid): New.
	(gomp_load_plugin_for_device): DLSYM_OPT the function 'get_uid'.
	(gomp_target_init): Set the device's 'uid' field to NULL.
	* testsuite/libgomp.c/device_uid.c: New test.
	* testsuite/libgomp.fortran/device_uid.f90: New test.