Whitelist aes and sha target_features?

[newpavlov]

I would like to use them in the RustCrypto project for conditional compilation. So if there is no particular reason against including them, it would be nice to have them.

This code currently does not work as intended:

#[cfg(target_feature="aes")]
fn main() {
    println!("aes enabled");
}

#[cfg(not(target_feature="aes"))]
fn main() {
    println!("aes disabled");
}

Related: #29717

[Mark-Simulacrum]

cc @BurntSushi and @alexcrichton

[alexcrichton]

Seems plausible to me!