googletest formatted tests are discovered by running the test executable.
Previously testing would silently succeed if the test executable crashed
during the discovery process. Now testing fails with "error: unable to
discover google-tests ..." if the test executable exits with a non-zero status.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280455 91177308-0d34-0410-b5e6-96231b3b80d8