Auto merge of #141415 - est31:let_chains_libcore, r=tgross35

Remove #![feature(let_chains)] from libcore

PR #132833 has stabilized the let_chains feature. This PR removes the last occurrence from the library.

Split out of #140966 as it caused breakage. Now we have a patch to the linux tree that fixes the build, so we update the linux tree to it.

cc Rust-for-Linux/linux#1163
cc #140722

Author: bors

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 +2,8 @@
 
 set -euo pipefail
 
-LINUX_VERSION=v6.15-rc4
+# https://github.com/Rust-for-Linux/linux/issues/1163
+LINUX_VERSION=3ca02fc80cc4fdac63aaa6796642f1e07be591d6
 
 # Build rustc, rustdoc, cargo, clippy-driver and rustfmt
 ../x.py build --stage 2 library rustdoc clippy rustfmt