Avoid false gethostname_used_without_requesting_gnulib_module_gethostname. * modules/gethostname (configure.ac): Invoke gl_MODULE_INDICATOR. * lib/unistd.in.h (gethostname): Don't define to gethostname_used_without_requesting_gnulib_module_gethostname if the gnulib module 'gethostname' is in use under the same configure.ac.