Fix the register scavenger for targets that provide custom spilling

As pointed out by Richard Sandiford, my recent updates to the register
scavenger broke targets that use custom spilling (because the new code assumed
that if there were no valid spill slots, than spilling would be impossible).

I don't have a test case, but it should be possible to create one for Thumb 1,
Mips 16, etc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178073 91177308-0d34-0410-b5e6-96231b3b80d8
TableGen SubtargetEmitter fix to allow A9 and Swift to coexist.

Allow variants to be defined only for some processors on a target.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178074 91177308-0d34-0410-b5e6-96231b3b80d8
Restore real bit lengths on PPC register numbers

As suggested by Bill Schmidt (in reviewing r178067), use the real register
number bit lengths (which is self-documenting, and prevents using illegal
numbers), and set only the relevant bits in HWEncoding (which defaults to 0).

No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178077 91177308-0d34-0410-b5e6-96231b3b80d8
Debug Info: Provide a means to update the members of a composite type

This will be used to factor out some uses of magic number operand offsets
inside Clang where these fields were updated in an effort to resolve forward
declarations/circular references.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178078 91177308-0d34-0410-b5e6-96231b3b80d8