clang-format: Slightly adapt decision of when to break before <<.

Before:
  Diag(aaaaaaaaaaaaaaaaaaaa, aaaaaaaa) << aaaaaaaaaaaaaaaaaaaaaaaaa(
                                              aaaaaaaaaaaaa);

After:
  Diag(aaaaaaaaaaaaaaaaaaaa, aaaaaaaa)
      << aaaaaaaaaaaaaaaaaaaaaaaaa(aaaaaaaaaaaaa);

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@197690 91177308-0d34-0410-b5e6-96231b3b80d8