The first part of this patch (D101315) separates libomptarget tests into a lit instance per offloading target.
This allows to fuse the RUN lines for most tests.
This patch updates the RUN lines in libomptarget tests to use a generic run line independent of the offloading target selected for the lit instance.
In cases, where no RUN line was defined for a specific offloading target, the corresponding target is declared as XFAIL. If it turns out that a test actually supports the target, the XFAIL line can be removed.