Add 'libgomp.oacc-c-c++-common/private-atomic-1.c' [PR83812]

... to at least document/test/XFAIL nvptx offloading: PR83812 "operation not
supported on global/shared address space".

	libgomp/
	PR target/83812
	* testsuite/libgomp.oacc-c-c++-common/private-atomic-1.c: New.