Update NEWS to mention drive-by fix for bug 18699.

Wilco fixed this tilegx bug in commit fe8c2b33 ("Since we
now inline isinf, isnan and isfinite in math.h, replace uses
of __isinf_ns(l/f) with isinf, and remove the unused inlines
__isinf_ns(l/f), __isnan(f) and __finite(f).")

I verified that reverting math/s_cprojf.c back to using the
sysdeps/ieee754/flt-32/math_private.h version of __isinf_nsf()
instead of isinf() brings back the bug on tilegx.