ARM IAS: support .align without parameters

.align is handled specially on certain targets.  .align without any parameters
on ARM indicates a default alignment (4).  Handle the special case in the target
parser, but fall back to the generic parser for the normal version.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201988 91177308-0d34-0410-b5e6-96231b3b80d8
ARMAsmParser: whitespace

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201989 91177308-0d34-0410-b5e6-96231b3b80d8