make const_err a hard error

Author: RalfJung

tests/fail/erroneous_const.rs

@@ -3,7 +3,6 @@
 // Inlining changes the error location
 //@compile-flags: -Zmir-opt-level=0
 #![feature(never_type)]
-#![warn(warnings, const_err)]
 
 struct PrintName<T>(T);
 impl<T> PrintName<T> {

tests/fail/erroneous_const2.rs

@@ -1,13 +1,9 @@
 const X: u32 = 5;
 const Y: u32 = 6;
 const FOO: u32 = [X - Y, Y - X][(X < Y) as usize];
-//~^ERROR: any use of this value
-//~|WARN: previously accepted
+//~^ERROR: evaluation of constant value failed
 
 #[rustfmt::skip] // rustfmt bug: https://github.com/rust-lang/rustfmt/issues/5391
 fn main() {
-    println!("{}", FOO); //~ERROR: post-monomorphization error
-    //~|ERROR: evaluation of constant value failed
-    //~|ERROR: erroneous constant used
-    //~|WARN: previously accepted
+    println!("{}", FOO);
 }

tests/fail/erroneous_const2.stderr

@@ -1,39 +1,9 @@
-error: any use of this value will cause an error
-  --> $DIR/erroneous_const2.rs:LL:CC
-   |
-LL | const FOO: u32 = [X - Y, Y - X][(X < Y) as usize];
-   | --------------    ^^^^^ attempt to compute `5_u32 - 6_u32`, which would overflow
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
-   = note: `#[deny(const_err)]` on by default
-
 error[E0080]: evaluation of constant value failed
   --> $DIR/erroneous_const2.rs:LL:CC
    |
-LL |     println!("{}", FOO);
-   |                    ^^^ referenced constant has errors
-
-error: erroneous constant used
-  --> $DIR/erroneous_const2.rs:LL:CC
-   |
-LL |     println!("{}", FOO);
-   |                    ^^^ referenced constant has errors
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error: post-monomorphization error: referenced constant has errors
-  --> $DIR/erroneous_const2.rs:LL:CC
-   |
-LL |     println!("{}", FOO);
-   |                    ^^^ referenced constant has errors
-   |
-   = note: inside `main` at $DIR/erroneous_const2.rs:LL:CC
-
-note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+LL | const FOO: u32 = [X - Y, Y - X][(X < Y) as usize];
+   |                   ^^^^^ attempt to compute `5_u32 - 6_u32`, which would overflow
 
-error: aborting due to 4 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0080`.