* Convert to be a MachineFunctionPass instance

* Use new FunctionFrameInfo object to manage stack slots instead of doing
  it directly
* Adjust to new MRegisterInfo API
* Don't take a TM as a ctor argument
* Don't keep track of which callee saved registers are modified
* Don't emit prolog/epilog code or spill/restore code for callee saved regs
* Use new allocation_order_begin/end iterators to simplify dramatically the
  logic for picking registers to allocate
* Machine PHI nodes can no longer contain constant arguments

* Use a bitvector to keep track of registers used instead of a set
* Fix problem where explicitly referenced registers would be added to
  regsused set and never removed

llvm-svn: 5196