New module 'coshf'. * 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.