The combination of alloc_error_handler and target_features_11 is unsound

[veluca93]

The following code compiles:

#![feature(target_feature_11, alloc_error_handler)]

#[target_feature(enable = "avx")]
#[alloc_error_handler]
fn f(_: std::alloc::Layout) -> ! {
    panic!()
}

However, this is unsound if the allocation error handler is invoked on a machine that does not support avx.

The alloc_error_handler feature is still unstable, tracking issue: #51540

This issue emerged during the stabilization PR for target_features_11: #134090