Fourth part of NWFPE performance improvements, building on patch 1466/1.
 
This patch makes 80-bit (extended precision) a compile-time option in NWFPE.
The effect of the extra code path on 32/64 bit operations is not as significant
as I had first thought - speedup is between 0.7 and 1.5% depending on which
tree (rmk or nw) you do the changes in.  However the reduction in code size,
particularly when softfloat has the same functions cut out, may be of value
on embedded systems.