* lib/math.in.h (rintf): Test HAVE_DECL_RINTF, not HAVE_RINTF.
* m4/rintf.m4 (gl_FUNC_RINTF): Don't assume rintf() is declared when it
exists. Set HAVE_DECL_RINTF.
* m4/math_h.m4 (gl_MATH_H_DEFAULTS): Initialize HAVE_DECL_RINTF, not
HAVE_RINTF.
* modules/math (Makefile.am): Substitute HAVE_DECL_RINTF, not
HAVE_RINTF.
* doc/posix-functions/rintf.texi: Mention missing declaration problem.
* lib/math.in.h (rintf): New declaration.
* lib/rintf.c: New file.
* m4/rintf.m4: New file.
* m4/math_h.m4 (gl_MATH_H): Test whether rintf is declared.
(gl_MATH_H_DEFAULTS): Initialize GNULIB_RINTF, HAVE_RINTF.
* modules/math (Makefile.am): Substitute GNULIB_RINTF, HAVE_RINTF.
* modules/rintf: New file.
* tests/test-math-c++.cc: Check the declaration of rintf.
* doc/posix-functions/rintf.texi: Mention the new module.