rust: Ignore preserve-most functions

Neither bindgen nor Rust know about the preserve-most calling
convention, and Clang describes it as unstable. Since we aren't using
functions with this calling convention from Rust, blocklist them.

These functions are only added to the build when list hardening is
enabled, which is likely why others didn't notice this yet.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20231031201945.1412345-1-mmaurer@google.com


[ Used Markdown for consistency with the other comments in the file. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>