Stub out RegAllocGreedy.

This new register allocator is initially identical to RegAllocBasic, but it will
receive all of the tricks that RegAllocBasic won't get.

RegAllocGreedy will eventually replace linear scan.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121234 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed