pre-ll: Vertex & constant structs fields are re-ordered in rust 1.67 so don't work

[alexheretic]

GFX version: v0.18

Previously working code stops working properly with rust 1.67 (though still compiles).

gfx_defines! {
    vertex Vertex {
        ...
    }
    constant Props {
        ...
    }
    ...
}

This can be manually fixed by declaring #[repr(C)]

gfx_defines! {
    #[repr(C)]
    vertex Vertex {
        ...
    }
    #[repr(C)]
    constant Props {
        ...
    }
    ...
}

I think it would be nice to release a new version that will fix this without such intervention.

[alexheretic]

Resolved by #3791 #3792