Rollup merge of #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/rust#137531.

The modified test files are reported in rust-lang/rust#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