clang-format: Treat a trailing comment like a trailing comma in braced lists.

Before:
  static StructInitInfo module = {MODULE_BUILTIN, /* type */
                                  "streams" /* name */
  };

After:
  static StructInitInfo module = {
      MODULE_BUILTIN, /* type */
      "streams"       /* name */
  };

This fixes llvm.org/PR19378.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@205851 91177308-0d34-0410-b5e6-96231b3b80d8