Mutex and Condvar are being replaced by more efficient implementations, which need thread parking themselves (see rust-lang#93740). Therefore use the pthread synchronization primitives directly. Also, avoid allocating because the Parker struct is being placed in an Arc anyways.

…r=jackh726

Ensure that `'_` and GAT yields errors

Fixes rust-lang#95305

`@bors` r? `@jackh726`

…=manishearth

Add more diagnostic items

This just adds a handful diagnostic items I noticed were missing.

Would it be worth doing this for all of the remaining types? I'm willing to do it if it'd be helpful.

std: directly use pthread in UNIX parker implementation

`Mutex` and `Condvar` are being replaced by more efficient implementations, which need thread parking themselves (see rust-lang#93740). Therefore we should use the `pthread` synchronization primitives directly. Also, we can avoid allocating the mutex and condition variable because the `Parker` struct is being placed in an `Arc` anyways.

This basically is just a copy of the current `Mutex` and `Condvar` code, which will however be removed (again, see rust-lang#93740). An alternative implementation could be to use dedicated private `OsMutex` and `OsCondvar` types, but all the other platforms supported by std actually have their own thread parking primitives.

I used `Pin` to guarantee a stable address for the `Parker` struct, while the current implementation does not, rather using extra unsafe declaration. Since the thread struct is shared anyways, I assumed this would not add too much clutter while being clearer.

…davidtwco

Migrate ambiguous plus diagnostic to the new derive macro

r? ``@davidtwco`` ``@jyn514``

…-lifetime-suggestion, r=jackh726

Recover suggestions to introduce named lifetime under NLL

Fixes rust-lang#96157

r? `@jackh726`

Built on top of rust-lang#96385 so only the second commit is relevant

Fixed grammatical error in example comment

Added missing "we" in sentence.