constructor for bitfield unit with 64 bit wide bitfields fails to build on 32 bit

[heycam]

Input:

#include <stdint.h>

struct Test {
  uint64_t x : 56;
  uint64_t y : 8;
};

On 32 bit, rust-bindgen generates:

impl Test {
    ...
    #[inline]
    pub fn new_bitfield_1(
        x: u64,
        y: u64,
    ) -> __BindgenBitfieldUnit<[u8; 8usize], u64> {
        let mut __bindgen_bitfield_unit: __BindgenBitfieldUnit<
            [u8; 8usize],
            u64,
        > = Default::default();
        __bindgen_bitfield_unit.set(0usize, 56u8, {
            let x: [u32; 2usize] = unsafe { ::std::mem::transmute(x) };
            x as u64
        });
        __bindgen_bitfield_unit.set(56usize, 8u8, {
            let y: [u32; 2usize] = unsafe { ::std::mem::transmute(y) };
            y as u64
        });
        __bindgen_bitfield_unit
    }

This fails to compile with non-primitive cast: '[u32; 2usize]' as 'u64' errors.