Update tests/fail-dep/concurrency/libc_pthread_mutex_move.rs

Co-authored-by: Ralf Jung <post@ralfj.de>

tests/fail-dep/concurrency/libc_pthread_mutex_move.rs

@@ -22,7 +22,7 @@ fn check() {
         let mut m: libc::pthread_mutex_t = libc::PTHREAD_MUTEX_INITIALIZER;
         libc::pthread_mutex_lock(&mut m as *mut _);
 
-        let mut m2 = m;
+        let mut m2 = m; // move the mutex
         libc::pthread_mutex_unlock(&mut m2 as *mut _); //~[static_initializer] ERROR: pthread_mutex_t can't be moved after first use
     }
 }