Fix yet another unseen regression caused by r223113
r223113 added support for ARM modified immediate assembly syntax. Which
assumes all immediate operands are prefixed with a '#'. This assumption
is wrong as per the ARMARM - which recommends that all '#' characters be
treated optional. The current patch fixes this regression and adds a test
case. A follow-up patch will expand the test coverage to other instructions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223381
91177308-0d34-0410-b5e6-
96231b3b80d8