intent in cfg_layout_initialize

[DJ Delorie]

> passing CLEANUP_UPDATE_LIFE would work.
> You get the liveness invalidated when entering to cfglayout before
> sched2, right?

The problem shows up in 33.bbro.  Some conditional jumps are deleted,
but the life info for the register it's testing isn't updated or
propogated.

> I think best fix is to simply add parameter of cfglayout_initialize
> specifying whether the liveness shall be preserved, as for tracer
> the cfglayout_initialize is called before liveness is built.

The one that I'm seeing is the call from the start of
reorder_basic_blocks().