clang-format treats MSVC `__super` keyword like all other keywords adding
a single space after. This change disables this behavior for `__super`.

Patch originally by jutocz (thanks!).

Differential Revision: https://reviews.llvm.org/D30932

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@297936 91177308-0d34-0410-b5e6-96231b3b80d8