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