[ShrinkWrap] Teach ShrinkWrap to handle targets requiring a register scavenger.

The included test only checks for a compiler crash for now. Several people are
facing this issue, so we first resolve the crash, and will increase shrinkwrap's
coverage later in a follow-up patch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253718 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed