clang-format: Break default arguments less eagerly.

Before:
  void aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(int aaaaaaaaaaaaaaaaaaaaaaaaaaaa =
                                              1);

After:
  void aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
      int aaaaaaaaaaaaaaaaaaaaaaaaaaaa = 1);

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@198070 91177308-0d34-0410-b5e6-96231b3b80d8