filesystem tests are not yet supported when running tests on a remote board, because the testing infrastructure isn't quite ready for it yet. Supporting filesystem in the infrastructure is non-trivial, so I suggest disabling these tests for now.
Also, pass through LIT arguments to builtins and runtimes (they were not passed through before). I'm not sure about this change though, as we may want to differentiate between LIT arguments for llvm/clang tests from those for libunwind/libc++abi/libc++ tests. For example, we may want to specify a higher number of threads for the tests that are run remotely, as it significantly speeds up the test suite. Please let me know what you think.