Set the minimum required version of CMake high enough to avoid the
warning for CMAKE_LEGACY_CYGWIN_WIN32. The warning appears on stderr
and breaks the expected output matching.
Move the Tests/FPHSA_InvalidFOUND_VAR test case over to a new
RunCMake.FPHSA test with a BadFoundVar case. The RunCMake tests are
built to cover failure cases easily and robustly.