The ARM assembler allows register alias redefinitions as long as it
targets the same register. r222319 broke that. In the AArch64 case
it would just produce a new warning, but in the ARM case it would
error out on previously accepted assembler.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228109 91177308-0d34-0410-b5e6-96231b3b80d8