[lit] GoogleTest framework should report failures if test binary crashes

[lit] GoogleTest framework should report failures if test binary crashes

lit runs a gtest executable multiple times. First it runs it to
discover tests, then later it runs the executable again for each test.
However, if the discovery fails (perhaps because of a broken
executable), then no tests were previously run and no failures were
reported.  This patch creates a dummy test if discovery fails, which
will later fail when test are run and be reported as a failure.

Differential Revision: https://reviews.llvm.org/D80096