rustc staticlib bug

Cargo.toml

[package]
edition = "2018"
name = "hello_world"
version = "0.1.0"

[lib]
crate-type = ["staticlib"]
name = "hello_world"

[dependencies]
# Can be any crate really. Just needed something small.
bitflags = "1.1.0"

[profile.release]
lto = "thin"

lib.rs

#[macro_use]
extern crate bitflags;

bitflags! {
    struct Flags: u32 {
        const A = 0b00000001;
        const B = 0b00000010;
        const C = 0b00000100;
        const ABC = Self::A.bits | Self::B.bits | Self::C.bits;
    }
}

#[no_mangle]
pub extern "C" fn hello_world(x: usize) {
    let e1 = Flags::A | Flags::C;
    println!("oh hey there {} {:?}", x, Flags::empty());
}