Add an error message for using typeof instead of an ICE

[skeleten]

Fixes #29184

This adds an error message for the use of the reserved typeof keyword, instead of reporting an ICE.
Also adds a compile-fail test.

I chose to add a span_err instead of removing to parser code, as to preserve the reservation of typeof.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @arielb1 (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[alexcrichton]

Thanks! Could you also squash these down to one commit?

[skeleten]

I somehow seem to have screwed up my own fork. Mind If I close this, redo the stuff in a new fork, and open the PR again?

[arielb1]

@skeleten

Just squash the commits.

[skeleten]

@arielb1
Isn't as easy if it is your first time rebasing ;) I think I did it anyways :P

[steveklabnik]

@skeleten for reference: http://blog.steveklabnik.com/posts/2012-11-08-how-to-squash-commits-in-a-github-pull-request :)

[skeleten]

Thanks, that'll be helpful :)

[alexcrichton]

@bors: r+ 044a8fe

Thanks!

[bors]

⌛ Testing commit 044a8fe with merge 7ee4e9e...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt