Fix longjmp-across-rust test

Destructor are removed from stack because it's considered UB.

tests/run-make/longjmp-across-rust/main.rs

@@ -10,19 +10,11 @@ fn main() {
     }
 }
 
-struct A;
-
-impl Drop for A {
-    fn drop(&mut self) {}
-}
-
 extern "C" fn test_middle() {
-    let _a = A;
     foo();
 }
 
 fn foo() {
-    let _a = A;
     unsafe {
         test_end();
     }