Basic support for formatting for-loops.

We used to not really format them. Now we do:

  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
                                        SE = BB->succ_end();
       SI != SE; ++SI) {

This is just one example and I am sure we still mess some of them up, but it
is a step forward.

llvm-svn: 170899