#[repr(align(n), C)] and #[repr(packed, C)] are not represented correctly

[cyphar]

#[repr(align(n), C)] markers on a struct should be translated to __attribute__((align(n)), similarly for #[repr(packed, C)] for __attribute__((packed)). Right now they are generated as being opaque structs. This is necessary to implement a Rust-based __attribute__((packed)) (by setting #[repr(align(1))]).

Additionally, #[repr(align(n))] and #[repr(C)] separately applied on the same struct (which AFAIK is equivalent to #[repr(align(n), C)]) will result in the structure being generated as a non-opaque struct but with the wrong alignment (resulting in C code passing incorrect structs to Rust code -- which won't end well).