GlobalISel: support debug intrinsics.

The translation scheme is mostly cribbed from FastISel, and it's not entirely
convincing semantically. But it does seem to work in the common cases and allow
variables to be printed so it can't be all wrong.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293228 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed