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