Improve clang-format's stream formatting.

clang-format was a bit too aggressive when trying to keep labels and
values on the same line.

Before:
    llvm::outs()
         << "aaaaaaaaaaaaaaaaaaa: " << aaaaaaaaaaaaa(
                                           aaaaaaaaaaaaaaaaaaaaaaaaaaaa);
After:
  llvm::outs() << "aaaaaaaaaaaaaaaaaaa: "
               << aaaaaaaaaaaaa(aaaaaaaaaaaaaaaaaaaaaaaaaaaa);