This patch adds a run line to most libomptarget tests to also test the nvptx64 target, if available.
Adding $BUILD/lib to the LIBRARY_PATH fixes https://bugs.llvm.org/show_bug.cgi?id=46836.
I moved the existing runline for nvptx64 to the end. Lit will stop for the first failing runline and mark the test as failed. If the GPU is configured for exclusive mode, this line tends to fail quite often.
None of the newly enabled tests fail on my system.