88K changes inspired by Ted Lemon (uunet!lupine!mellon)

88K changes inspired by Ted Lemon (uunet!lupine!mellon)
* tm-m88k.h, tm-umax.h:  Avoid sizeof() in REGISTER_xxx macros,
since they define the target, not the host.
* m88k-pinsn.c:  Fix typo.

Patches by Paul Eggert <eggert@twinsun.com>.
* valarith.c (value_zerop):  -0.0 is still zero.
* eval.c (evaluate_subexp):  Avoid NaN anomalies in float compares.