* lib/math.in.h (expm1f): Override if REPLACE_EXPM1F is 1.
* m4/expm1f.m4 (gl_FUNC_EXPM1F_WORKS): New macro.
(gl_FUNC_EXPM1F): Invoke it. Set REPLACE_EXPM1F to 1 if expm1f() does
not work.
* m4/math_h.m4 (gl_MATH_H_DEFAULTS): Initialize REPLACE_EXPM1F.
* modules/math (Makefile.am): Substitute REPLACE_EXPM1F.
* modules/expm1f (configure.ac): Consider REPLACE_EXPM1F.
(Depends-on): Update conditions.
* doc/posix-functions/expm1f.texi: Mention the IRIX 6.5 bug.