How does a C-style struct with a bitfield get represented in a Rust #[repr(C)] struct?

I have a C struct defined as:

struct my_c_s {
    u_char          *ptr;
    unsigned        flag_a:1;
    unsigned        flag_b:1;
    int             some_num;
}

How would flag_a and flag_b be represented?

#[repr(C)]
pub struct my_rust_s {
    pub ptr: *const u_char,
    //pub flag_a: ?,
    //pub flag_b: ?,
    pub some_num: ::libc::c_int,
}

Can I declare them as bools? Or does that whole thing need to be some sort of set of bits with a single field, and then I bitmask them out?

e.g. pub flag_bits: ::libc::c_uint,