Missing max_atomic_width in spec.

[m-ou-se]

The avr-unknown-unknown target now specifies no max_atomic_width, which means it falls back to the pointer size of 16 bits:

    let target = rustc_target::spec::TargetTriple::from_triple("avr-unknown-unknown");
    println!("{}", rustc_target::spec::Target::search(&target).unwrap().max_atomic_width());
    // output: 16

Is this correct? As far as I know, AVR does not have any (atomic) 16-bit operations.

[m-ou-se]

Moved to rust repository: rust-lang#76363