Rewrite some jump.c routines to use flags

[Eric Botcazou]

> AIUI, neither ORDERED nor UNEQ trap on signalling NaNs.  Without this,
> the follow-on patch would fold
> 
>    (and (ordered x y) (uneq x y)) -> (eq x y)
> 
> which is the same thing for quiet NaNs but not for signalling NaNs.

Note that GCC defaults to -fno-signaling-nans and the transformation would be 
valid in this mode.

-- 
Eric Botcazou