[ms-inline asm] Add support for detecting simple ms-style inline asm. Simple

[ms-inline asm] Add support for detecting simple ms-style inline asm.  Simple
asm statements are those that don't reference variable names, function names,
and labels.

Add logic to generate a patched AsmString that will eventually be consumed by
the AsmParser.  No functional change at this point, so unfortunately no test
case.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@161508 91177308-0d34-0410-b5e6-96231b3b80d8