kbuild: rust: use `-Zdwarf-version` to support DWARFv5

Rust 1.64.0 introduced (unstable) support for the `-Zdwarf-version`
flag, which allows to select DWARFv5, thus use it.

Link: https://github.com/rust-lang/rust/issues/103057
Link: https://github.com/rust-lang/rust/pull/98350


Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20240217002602.57270-1-ojeda@kernel.org


Signed-off-by: Miguel Ojeda <ojeda@kernel.org>