* lib/math.in.h (setpayloadsigl): New declaration.
* lib/setpayloadsigl.c: New file, based on lib/setpayloadl.c.
* m4/math_h.m4 (gl_MATH_H): Test whether setpayloadsigl is declared.
(gl_MATH_H_REQUIRE_DEFAULTS): Initialize GNULIB_SETPAYLOADSIGL.
(gl_MATH_H_DEFAULTS): Initialize HAVE_SETPAYLOADSIGL.
* modules/math (Makefile.am): Substitute GNULIB_SETPAYLOADSIGL,
HAVE_SETPAYLOADSIGL.
* modules/setpayloadsigl: New file.
* doc/posix-functions/setpayloadsigl.texi: Mention the new module.