Don't use a char that's already used within the expr

Author: oberien

src/test/run-pass/weird-exprs.rs

@@ -113,7 +113,7 @@ fn union() {
 }
 
 fn special_characters() {
-    let val = !((|(..):(_,_),__@_|__)((&*"\\",'@')/**/,{})=={&[..=..][..];})//
+    let val = !((|(..):(_,_),__@_|__)((&*"\\",'🤔')/**/,{})=={&[..=..][..];})//
     ;
     assert!(!val);
 }