rust: Enable type_alias_impl_trait

This is required to make PinInit<T> work as a return value from a
trait function. We indirect via an associated type to avoid
return_position_impl_trait_in_trait, which is an incomplete feature.

Signed-off-by: Asahi Lina <lina@asahilina.net>

Author: hoshinolina

rust/kernel/lib.rs

@@ -21,6 +21,7 @@
 #![feature(ptr_sub_ptr)]
 #![feature(sized_type_properties)]
 #![feature(slice_range)]
+#![feature(type_alias_impl_trait)]
 #![feature(unsize)]
 #![allow(stable_features)]
 // Stable in Rust 1.83

scripts/Makefile.build

@@ -248,7 +248,7 @@ $(obj)/%.lst: $(obj)/%.c FORCE
 # Compile Rust sources (.rs)
 # ---------------------------------------------------------------------------
 
-rust_allowed_features := arbitrary_self_types,lint_reasons
+rust_allowed_features := arbitrary_self_types,lint_reasons,type_alias_impl_trait
 
 # `--out-dir` is required to avoid temporaries being created by `rustc` in the
 # current working directory, which may be not accessible in the out-of-tree