clang-format: Add space in corner case.

Before:
  SomeType s __attribute__((unused))(InitValue);
After:
  SomeType s __attribute__((unused)) (InitValue);

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186535 91177308-0d34-0410-b5e6-96231b3b80d8