illumos gate

In both strtod(3c) and wcstod(3c) man pages there is this wording:

       If the correct value is outside the range of representable values,
       ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL is returned (according to the sign
       of the value), a floating point overflow exception is raised, and errno
       is set to ERANGE.

The problem is that those constants (HUGE_VAL, HUGE_VALF, and HUGE_VALL) are not readily available when there is just stdlib.h or wchar.h included respectively (as suggested by the man pages synopsis) because they are defined in math.h, but math.h is not mentioned anywhere in either man page. We should change that.