[ms-inline asm] Move the immediate asm rewrite into the target specific
logic as a QOI cleanup.  No functional change.  Tests already in place.
rdar://13456414

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177446 91177308-0d34-0410-b5e6-96231b3b80d8