[TargetPassConfig] Add a hook to tell whether GlobalISel should warm on fallback.

Thanks to this patch, we know have a way to easly see if GlobalISel
failed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280273 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed