clang-format: Avoid line breaks before the first <<.

This puts a slight penalty on the linebreak before the first "<<", so
that clang-format generally tries to keep things on the first line.

User feedback has shown that this is generally desirable.

Before:
  llvm::outs()
      << "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa =" << aaaaaaaaaaaaaaaaaaaaaaaaaaa;

After:
  llvm::outs() << "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa ="
               << aaaaaaaaaaaaaaaaaaaaaaaaaaa;