Read BuildID on Linux about build_id HOT 1 OPEN

Thanks for the link @xfbs. Looks like this should work https://play.rust-lang.org/?gist=146b1d688012d40303d17f6848eabb52

#[link_section = ".note.gnu.build-id"]
static BUILD_ID: [u8; 0] = [];

fn main() {
    let build_id: [u8; 20] = unsafe { *BUILD_ID.as_ptr().offset(-20).cast() };
    println!("{:?}", build_id);
}

Worth checking that it matches what any other tools output. Also would be good to understand how widely ".note.gnu.build-id" is supported and if we can constrain usage of this technique to those targets where ".note.gnu.build-id" is practically guaranteed.

from build_id.