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`.

Rollup of 7 pull requests

Successful merges:

 - #67722 (Minor: note how Any is an unsafe trait in SAFETY comments)
 - #68586 (Make conflicting_repr_hints a deny-by-default c-future-compat lint)
 - #68598 (Fix null synthetic_implementors error)
 - #68603 (Changelog: Demonstrate final build-override syntax)
 - #68609 (Set lld flavor for MSVC to link.exe)
 - #68611 (Correct ICE caused by macros generating invalid spans.)
 - #68627 (Document that write_all will not call write if given an empty buffer)

Failed merges:

r? @ghost

Add an option to use LLD to link the compiler on Windows platforms

Based on #68609.

Using LLD is good way to improve compile times on Windows since `link.exe` is quite slow. The time for `x.py build --stage 1 src/libtest` goes from 0:12:00 to 0:08:29. Compile time for `rustc_driver` goes from 226.34s to 18.5s. `rustc_macros` goes from 28.69s to 7.7s. The size of `rustc_driver` is also reduced from 83.3 MB to 78.7 MB.

r? @Mark-Simulacrum