Add out-of-memory language item

[jlamb-at-polysync]

See this issue: rust-lang/rust#50144

Add something like this for oom() in sel4-entry:

#[lang = "oom"]
pub extern fn oom() -> ! {
    use core::fmt::Write;
    let _ = write!(
        sel4_sys::DebugOutHandle,
        "----- aborting from out-of-memory -----\n"
    );
    unsafe {
        core::intrinsics::abort();
    }
}