Add test for passing promotion but failing compilation

Author: oli-obk

src/test/ui/consts/rfc-2203-const-array-repeat-exprs/migrate-fail2.rs

@@ -0,0 +1,17 @@
+// ignore-compare-mode-nll
+// compile-flags: -Z borrowck=migrate
+// build-fail
+#![feature(const_in_array_repeat_expressions, const_panic, const_fn)]
+#![allow(warnings)]
+
+// Some type that is not copyable.
+struct Bar;
+
+const fn bad_bar() -> Bar { panic!() }
+//~^ ERROR evaluation of constant value failed
+
+fn main() {
+    let arr: [Bar; 2] = [bad_bar(); 2];
+    //~^ ERROR erroneous constant used
+    //~| ERROR evaluation of constant expression failed
+}

src/test/ui/consts/rfc-2203-const-array-repeat-exprs/migrate-fail2.stderr

@@ -0,0 +1,27 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/migrate-fail2.rs:10:29
+   |
+LL | const fn bad_bar() -> Bar { panic!() }
+   |                             ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/migrate-fail2.rs:10:29
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0080]: evaluation of constant expression failed
+  --> $DIR/migrate-fail2.rs:14:25
+   |
+LL |     let arr: [Bar; 2] = [bad_bar(); 2];
+   |                         ^---------^^^^
+   |                          |
+   |                          referenced constant has errors
+
+error: erroneous constant used
+  --> $DIR/migrate-fail2.rs:14:25
+   |
+LL |     let arr: [Bar; 2] = [bad_bar(); 2];
+   |                         ^^^^^^^^^^^^^^ referenced constant has errors
+   |
+   = note: `#[deny(const_err)]` on by default
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0080`.