[PATCH 2/7] rust: add derive macro for `Zeroable`

[Alice Ryhl]

Benno Lossin <benno.lossin@xxxxxxxxx> writes:
> Add a derive proc-macro for the `Zeroable` trait. The macro supports
> structs where every field implements the `Zeroable` trait. This way
> `unsafe` implementations can be avoided.
> 
> The macro is split into two parts:
> - a proc-macro to parse generics into impl and ty generics,
> - a declarative macro that expands to the impl block.
> 
> Suggested-by: Asahi Lina <lina@xxxxxxxxxxxxx>
> Signed-off-by: Benno Lossin <benno.lossin@xxxxxxxxx>

Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>