Some types of Write instances have a semantic meaning associated with
writing an empty buffer, such as sending an empty packet. This works
when calling `write` directly, and supplying an empty buffer. However,
calling `write_all` on an empty buffer will simply never call `write`,
because `write_all` assumes it has no work to do.

Document this behavior, to help prospective users of
datagram-packet-style Write instances.

… r=Mark-Simulacrum

Minor: note how Any is an unsafe trait in SAFETY comments

Motivation: helpful to people like myself reading the standard library source to better understand how to use Any, especially if we do go ahead with rust-lang#67562 and make it an unsafe trait.

Make conflicting_repr_hints a deny-by-default c-future-compat lint

Closes rust-lang#68428.
cc rust-lang#68585.

r? @petrochenkov @pnkfelix

…mplementors, r=ollie27

Fix null synthetic_implementors error

Fixes rust-lang#68584.

r? @ollie27

cc @kinnison

Changelog: Demonstrate final build-override syntax

Set lld flavor for MSVC to link.exe

This enables linking with LLD on Windows with just `-C linker=rust-lld` instead of needing `-C linker=rust-lld -C linker-flavor=lld-link`.

Correct ICE caused by macros generating invalid spans.

Closes rust-lang#68605

…n-DPC

Document that write_all will not call write if given an empty buffer

Some types of Write instances have a semantic meaning associated with
writing an empty buffer, such as sending an empty packet. This works
when calling `write` directly, and supplying an empty buffer. However,
calling `write_all` on an empty buffer will simply never call `write`,
because `write_all` assumes it has no work to do.

Document this behavior, to help prospective users of
datagram-packet-style Write instances.