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.