Tweak last commit.

Tweak last commit.

* lib/sethostname.c: Don't include <string.h>.
(sethostname): No need to copy the argument string to the stack. Don't
call clearerr. Preserve errno when fprintf failed.
* m4/sethostname.m4 (gl_FUNC_SETHOSTNAME): Comment about HOST_NAME_MAX.
Don't invoke AC_REPLACE_FUNCS.
* modules/sethostname (Link): Remove empty section.
* doc/glibc-functions/sethostname.texi: Gnulib does not fix the ENOSYS
failure problem.