Use cfg_attr like other items

Author: dholroyd

src/unix/bsd/mod.rs

@@ -594,10 +594,10 @@ extern {
     pub fn recvmsg(fd: ::c_int, msg: *mut ::msghdr, flags: ::c_int)
                    -> ::ssize_t;
 
-    #[cfg(not(target_os = "macos"))]
+    #[cfg_attr(not(target_os = "macos"))]
     pub fn sendmmsg(sockfd: ::c_int, msgvec: *mut ::mmsghdr, vlen: ::c_uint,
                     flags: ::c_int) -> ::c_int;
-    #[cfg(not(target_os = "macos"))]
+    #[cfg_attr(not(target_os = "macos"))]
     pub fn recvmmsg(sockfd: ::c_int, msgvec: *mut ::mmsghdr, vlen: ::c_uint,
                     flags: ::c_int, timeout: *mut ::timespec) -> ::c_int;