Make test order-independent.

Author: cjgillot

tests/codegen/iter-repeat-n-trivial-drop.rs

@@ -33,7 +33,7 @@ pub fn iter_repeat_n_next(it: &mut std::iter::RepeatN<NotCopy>) -> Option<NotCop
 
     // CHECK: [[EMPTY]]:
     // CHECK-NOT: br
-    // CHECK: phi i16 [ undef, %start ], [ %[[VAL]], %[[NOT_EMPTY]] ]
+    // CHECK: phi i16
     // CHECK-NOT: br
     // CHECK: ret