[ms-inline asm] Address the FIXME for ImmDisp before brackets. This
is a follow on to r179393 and r179399.  Test case to be added on
the clang side.
Part of rdar://13453209


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179403 91177308-0d34-0410-b5e6-96231b3b80d8