Avoid allocating a flonum object for floating-opint calculations
that are consumed only by other floating-point caculations.
For this first cut, unboxing applies only to fl+, fl-, fl*, fl/,
flabs, fl<, fl<=, fl=, fl>, fl>=, bytevector-ieee-double-[native-]ref,
and bytevector-ieee-double-[native-]set!. Local variables can be
unboxed in the same way as implicit temporaries, and loop arguments
can be unboxed, but values in a closure and function-call arguments
are always boxed.
arm32 support is mostly in place, but not yet right. ppc32 support is
not yet implemented.
This commit includes a small change that is incompatible with previous
Chez Scheme versions: `(fl= +nan.0)` (and similar for other
comparisons) produces true instead of false.
original commit: 36459e43f10705aa3e383376ca7d54cf2998b7ee
7768b09118