[TargetPassConfig] Add a target hook to know what GlobalISel should do on error.

By default, this hook tells GlobalISel to abort (report a fatal error)
when it encounters an error. The alternative will be to fall back on
SDISel.
This fall back will be removed when the bring-up of GlobalISel is over.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279879 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed