clang-format: Fix overloading "operator," definitions more thoroughly.

Before:
  aaaaaaaaaaaaaaaaaaaaaa operator,(aaaaaaaaaaaaaaaaaaaaa &
                                   aaaaaaaaaaaaaaaaaaaaaaaaaa) const;
After:
  aaaaaaaaaaaaaaaaaaaaaa operator,(
      aaaaaaaaaaaaaaaaaaaaa &aaaaaaaaaaaaaaaaaaaaaaaaaa) const;

llvm-svn: 257330