Add sethostname for freebsdlike operating systems

src/unix/bsd/freebsdlike/mod.rs

@@ -811,6 +811,7 @@ extern {
                                      clock_id: *mut clockid_t) -> ::c_int;
     pub fn pthread_condattr_setclock(attr: *mut pthread_condattr_t,
                                      clock_id: clockid_t) -> ::c_int;
+    pub fn sethostname(name: *const ::c_char, len: ::c_int) -> ::c_int;
 }
 
 cfg_if! {