* lib/math.in.h (atan2f): New declaration.
* lib/atan2f.c: New file.
* m4/atan2f.m4: New file.
* m4/math_h.m4 (gl_MATH_H): Test whether atan2f is declared.
(gl_MATH_H_DEFAULTS): Initialize GNULIB_ATAN2F, HAVE_ATAN2F.
* modules/math (Makefile.am): Substitute GNULIB_ATAN2F, HAVE_ATAN2F.
* modules/atan2f: New file.
* tests/test-math-c++.cc: Check the declaration of atan2f.
* doc/posix-functions/atan2f.texi: Mention the new module.