Change to disable mir-opt in compile-flags

Author: JCTyblaidd

tests/compile-fail/data_race/read_write_race_stack.rs

@@ -1,5 +1,5 @@
 // ignore-windows: Concurrency on Windows is not supported yet.
-// compile-flags: -Zmiri-disable-isolation
+// compile-flags: -Zmiri-disable-isolation -Zmir-opt-level=0
 
 use std::thread::{spawn, sleep};
 use std::ptr::null_mut;
@@ -40,9 +40,7 @@ pub fn main() {
 
             sleep(Duration::from_millis(1000));
 
-            // Read, the add 1 fixes -Z mir-opt-level=3 from removing the read via dest-prop and breaking
-            // the test.
-            stack_var + 1 //~ ERROR Data race detected between Read on Thread(id = 1) and Write on Thread(id = 2)
+            stack_var //~ ERROR Data race detected between Read on Thread(id = 1) and Write on Thread(id = 2)
         });
 
         let j2 = spawn(move || {