The PTX md file goes to a lot of effort handling SC and DC movs, including for 
unspecs to mov low and high parts around.  However, these code paths are not 
exercised in any gcc test or the build of newlib.  The generic handling of these 
movs deals with type punning, (using the stack frame, if needed).  There 
doesn't appear a need for a separate punbuffer.

Thus this patch deletes a lot of that machinery.

nathan