this is a reworking of my recent return value patch.  this patch just contains 
changes to select which register contains a pointer value, and how structure 
return values are located.

I've added tdep field 'ptr_value_regnum' to accommodate the different ABIs that 
return in %d0 or %a0.

Most of the patch is adding the necessary pieces to the os sniffers to 
initialize that value.

ok?

nathan
-- 
Nathan Sidwell    ::   http://www.codesourcery.com   ::         CodeSourcery
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