Remove #![feature(let_chains)] from libcore

Author: est31

library/core/src/lib.rs

@@ -158,7 +158,6 @@
 #![feature(intra_doc_pointers)]
 #![feature(intrinsics)]
 #![feature(lang_items)]
-#![feature(let_chains)]
 #![feature(link_llvm_intrinsics)]
 #![feature(macro_metavar_expr)]
 #![feature(marker_trait_attr)]

src/ci/docker/scripts/rfl-build.sh

@@ -2,7 +2,7 @@
 
 set -euo pipefail
 
-LINUX_VERSION=v6.15-rc4
+LINUX_VERSION=3ca02fc80cc4fdac63aaa6796642f1e07be591d6 # https://github.com/Rust-for-Linux/linux/issues/1163
 
 # Build rustc, rustdoc, cargo, clippy-driver and rustfmt
 ../x.py build --stage 2 library rustdoc clippy rustfmt