Exit when there are unmatched delims to avoid noisy diagnostics

tests/ui/parser/do-not-suggest-semicolon-before-array.rs

@@ -2,7 +2,7 @@ fn foo() {}
 
 fn bar() -> [u8; 2] {
     foo()
-    [1, 3) //~ ERROR expected one of `.`, `?`, `]`, or an operator, found `,`
+    [1, 3) //~ ERROR mismatched closing delimiter
 }
 
 fn main() {}