When the register allocator runs out of registers, spill a physical register around...

When the register allocator runs out of registers, spill a physical register around the def's and use's of the interval being allocated to make it possible for the interval to target a register and spill it right away and restore a register for uses. This likely generates terrible code but is before than aborting.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48218 91177308-0d34-0410-b5e6-96231b3b80d8