libgomp.c-c++-common/metadirective-1.c: Expect 'error:' for nvptx compile [PR118694]

libgomp.c-c++-common/metadirective-1.c: Expect 'error:' for nvptx compile [PR118694]

OpenMP's 'target teams' is strictly coupled with 'teams'; if the latter
exists, the kernel is launched in directly with multiple teams. Thus,
the host has to know whether the teams construct exists or not. For

   #pragma omp target
     #pragma omp metadirective when (device={arch("nvptx")}: teams loop)

it is simple when 'nvptx' offloading is not supported, otherwise it depends
on the default device at runtime as the user code asks for a single team for
host fallback and gcn offload and multiple for nvptx offload.

In any case, this commit ensures that no FAIL is printed, whatever a
future solution might look like. Instead of a dg-bogus combined with an
'xfail offload_target_nvptx', one an also argue that a dg-error for
'target offload_target_nvptx' would be more appropriate.

libgomp/ChangeLog:

	PR middle-end/118694
	* testsuite/libgomp.c-c++-common/metadirective-1.c: xfail when
	compiling (also) for nvptx offloading as an error is then expected.