Automatically munch semicolons after blocks.

While it is mostly a user error to have the extra semicolon,
formatting it graciously will correctly format in the cases
where we do not fully understand the code (macros).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192543 91177308-0d34-0410-b5e6-96231b3b80d8