One of the painful aspects of all this code is the amount of target
dependent bits that have to be written and tested.

I didn't want to be scanning assembly code or RTL for prologues.  Each
target would have to have its own scanner which was too painful to
contemplate.

So instead I settled on having a routine that the target dependent
prologue expanders could call to dump information about what they were
doing.

This greatly simplifies the testing side of things by having a standard
way to dump decisions.  When combined with the dejagnu routines from
patch #1 which describe key attributes of the target's prologue
generation I can write tests in a fairly generic way.

This will be used by every target dependent prologue expander in this
series.

Comments/Questions?  OK for the trunk?