When global-isel fails on a MachineFunction MF, MF will be cleaned up
and given to SDISel.
Thanks to this fallback, we can already perform correctness test even if
we support only a small portion of the functions in a test.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279891 91177308-0d34-0410-b5e6-96231b3b80d8
