* m4/math_h.m4 (gl_MATH_H): Check for bug.
(gl_MATH_H_DEFAULTS): Set up default.
* modules/math (Makefile.am): Replace new indicators.
* lib/math.in.h (NAN, HUGE_VAL): Provide replacements.
* tests/test-math.c (main): Test this.
* m4/strtod.m4 (gl_FUNC_STRTOD): Don't rely on HUGE_VAL.
* doc/posix-headers/math.texi (math.h): Mention bug.
Reported by Nelson H. F. Beebe and Jim Meyering.