Extend well-known traits by Unpin

[memoryleak47]

I read the RFC and didn't find any special rules concerning Unpin, so this one is rather straight-forward. Correct me if I missed something!
cc #363

[jackh726]

I don't think this is right. I think Unpin needs to be implemented for all the built in types. Std has impls for all scalars, ref, raws; but we need builtin impls for function pointers, function defs, arrays, str, closures, slices(?).

[jackh726]

Also, please update the well known traits table in the book.

[memoryleak47]

I thought this was a consequence of defining it as an auto trait. I'll look into it.

[bors]

☔ The latest upstream changes (presumably #602) made this pull request unmergeable. Please resolve the merge conflicts.

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[jackh726]

LGTM! Pretty straightfoward until we get generators and auto traits for builtin types.

[jackh726]

@bors r+

[bors]

📋 Looks like this PR is still in progress, ignoring approval.

Hint: Remove [WIP] from this PR's title when it is ready for review.

[jackh726]

@bors r+

[bors]

📌 Commit c25997c has been approved by jackh726

[bors]

⌛ Testing commit c25997c with merge 01b4bff...

[bors]

☀️ Test successful - checks-actions
Approved by: jackh726
Pushing 01b4bff to master...