Add T: ?Sized to mem::align_of

[overlookmotel]

This is a repeat of #50948.

That issue was closed due to "this bound is still necessary until we've sorted out the custom DST traits". But that was in 2018, so I wondered if this blocker still persists?

[Noratrieb]

rust-lang/rfcs#3319 is relevant here and would allow replacing it with T: ?Sized + Aligned.

This would still not allow align_of::<dyn Debug>, which is fundamentally unsolvable.

[overlookmotel]

Thanks very much for coming back so swiftly. I wasn't aware that this was currently in motion.

Shall I leave this issue open for when/if Aligned trait is implemented?

[Dylan-DPC]

When the RFC is accepted, a tracking issue will be created which will track the progress of it. So we don't need to keep this issue open as it will likely be forgotten that it exists in future, so I am closing this.