Fix clippy tests

tests/ui/auxiliary/proc_macro_attr.rs

@@ -3,6 +3,7 @@
 
 #![crate_type = "proc-macro"]
 #![feature(repr128, proc_macro_hygiene, proc_macro_quote, box_patterns)]
+#![allow(incomplete_features)]
 #![allow(clippy::useless_conversion)]
 
 extern crate proc_macro;

tests/ui/auxiliary/proc_macro_derive.rs

@@ -3,6 +3,7 @@
 
 #![crate_type = "proc-macro"]
 #![feature(repr128, proc_macro_quote)]
+#![allow(incomplete_features)]
 
 extern crate proc_macro;
 

tests/ui/crashes/auxiliary/proc_macro_crash.rs

@@ -6,6 +6,7 @@
 // contain a proc-macro.
 
 #![feature(repr128)]
+#![allow(incomplete_features)]
 #![crate_type = "proc-macro"]
 
 extern crate proc_macro;