Add new TargetLowering code to provide the final register type that an

Add new TargetLowering code to provide the final register type that an
illegal value type will be transformed to, for code that needs the
register type after all transformations instead of just after the first
transformation.

Factor out the code that uses this information to do copy-from-regs and
copy-to-regs for various purposes into separate functions so that they
are done consistently.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37781 91177308-0d34-0410-b5e6-96231b3b80d8