alloc_error_handler feature no longer necessary

[bjorn3]

It's use was removed in #426.

linux/rust/kernel/lib.rs

Line 17 in 4d68cd7

alloc_error_handler,

[bjorn3]

I also can't easily find a use of concat_idents.

[wedsonaf]

I also can't easily find a use of concat_idents.

It's used in binder:

linux/drivers/android/defs.rs

Line 12 in 4d68cd7

$(pub const $newname: u32 = concat_idents!($prefix, $newname);)+

[bjorn3]

I see. It should be possible to implement concat_idents! with a proc_macro to avoid this unstable feature. (Choose the span of either inputs and then call Ident::new with this span and the concatenated ident name.)

[ojeda]

Thanks for catching that @bjorn3.

I also can't easily find a use of concat_idents.

For the features, I keep track of them in #2 (with where they are used).