Convert flag_finite_math_only uses in frange to HONOR_*.

As mentioned earlier, we should be using HONOR_* on types rather than
flag_finite_math_only.

gcc/ChangeLog:

	* value-range.cc (frange::set): Use HONOR_*.
	(frange::verify_range): Same.
	* value-range.h (frange_val_min): Same.
	(frange_val_max): Same.