Make sure the assembler-with-cpp hack for "#" works with multiple "#"s in
succession. Fixes PR16363.

Merged from r184240
Author: Eli Friedman <eli.friedman@gmail.com>
Date:   Tue Jun 18 21:33:38 2013 +0000

git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_33@186204 91177308-0d34-0410-b5e6-96231b3b80d8