clang-format: Fix template declaration line breaking with comment.

Before, clang-format would always insert a linebreak before the comment
in code like:
  template <typename T> // T can be A, B or C.
  struct S {};

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192297 91177308-0d34-0410-b5e6-96231b3b80d8