Auto merge of #144117 - nikic:llvm-21-host, r=<try>

Update dist-x86_64-linux host toolchain to LLVM 21

This updates the host clang used to build LLVM, as well as llvm-bolt. This avoids the bolt miscompile encountered in #144116.

r? `@ghost`

Author: rust-bors[bot]

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

@@ -5,7 +5,7 @@ set -ex
 source shared.sh
 
 # Try to keep the LLVM version here in sync with src/ci/scripts/install-clang.sh
-LLVM=llvmorg-20.1.0-rc2
+LLVM=llvmorg-21.1.0-rc1
 
 mkdir llvm-project
 cd llvm-project