* libm/mathfp/s_frexp.c: Check for special values on
the original input, not the manipulated output value.
* libm/mathfp/sf_frexp.c: Ditto.
* libm/mathfp/s_atangent.c: Don't use local value branch
when checking for quadrant.
* libm/mathfp/sf_atangent.c: Ditto.