Only warn on erroneous promoted constants

src/test/ui/const-eval/conditional_array_execution.stderr

@@ -1,17 +1,14 @@
 warning: attempt to subtract with overflow
-  --> $DIR/conditional_array_execution.rs:13:19
+  --> $DIR/conditional_array_execution.rs:15:19
    |
 LL | const FOO: u32 = [X - Y, Y - X][(X < Y) as usize];
    |                   ^^^^^
    |
    = note: #[warn(const_err)] on by default
 
-error[E0080]: constant evaluation error
-  --> $DIR/conditional_array_execution.rs:17:20
+warning: constant evaluation error
+  --> $DIR/conditional_array_execution.rs:19:20
    |
-LL |     println!("{}", FOO); //~ E0080
+LL |     println!("{}", FOO);
    |                    ^^^ referenced constant has errors
 
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0080`.