Rollup merge of rust-lang#143329 - folkertdev:minicore-diagnostic-on-unimplemented, r=jieyouxu

minicore: use core's `diagnostic::on_unimplemented` messages

Without these attributes, the error message is different. Keeping the diagnostics up-to-date seems related to rust-lang#137531.

The modified test files are reported in rust-lang#143319 as failing for `--target=riscv64gc-unknown-linux-gnu`. Using `minicore` for them makes it easier to troubleshoot this sort of issue.

r? ``@jieyouxu``

Author: jdonszelmann

core/src/marker.rs

@@ -19,6 +19,9 @@ use crate::fmt::Debug;
 use crate::hash::{Hash, Hasher};
 use crate::pin::UnsafePinned;
 
+// NOTE: for consistent error messages between `core` and `minicore`, all `diagnostic` attributes
+// should be replicated exactly in `minicore` (if `minicore` defines the item).
+
 /// Implements a given marker trait for multiple types at the same time.
 ///
 /// The basic syntax looks like this: