XFAIL OpenMP/nvptx execution-time hangs for simple nested OpenMP 'target'/'parallel...

XFAIL OpenMP/nvptx execution-time hangs for simple nested OpenMP 'target'/'parallel'/'task' constructs [PR99555]

... still awaiting proper resolution, of course.

	libgomp/
	PR target/99555
	* testsuite/lib/libgomp.exp
	(check_effective_target_offload_device_nvptx): New.
	* testsuite/libgomp.c/pr99555-1.c <nvptx offload device>: Until
	resolved, make sure that we exit quickly, with error status,
	XFAILed.
	* testsuite/libgomp.c-c++-common/task-detach-6.c: Likewise.
	* testsuite/libgomp.fortran/task-detach-6.f90: Likewise.