Rollup merge of #80780 - lianghanzhen:master, r=petrochenkov

Return EOF_CHAR constant instead of magic char.

compiler/rustc_lexer/src/cursor.rs

@@ -33,7 +33,7 @@ pub(crate) fn prev(&self) -> char {
 
         #[cfg(not(debug_assertions))]
         {
-            '\0'
+            EOF_CHAR
         }
     }