Update code base to use LLVM 21 (#434)

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Co-authored-by: LJ <81748770+elle-j@users.noreply.github.com>
Co-authored-by: xermicus <cyrill@parity.io>

.github/workflows/test-llvm-builder.yml

@@ -33,7 +33,7 @@ jobs:
       - name: Install Dependencies
         if: matrix.runner == 'parity-large'
         run: |
-          sudo apt update && sudo apt-get install -y cmake ninja-build curl git libssl-dev pkg-config clang lld musl
+          sudo apt update && sudo apt-get install -y cmake ninja-build curl git libssl-dev pkg-config clang lld musl xz-utils build-essential
 
       - name: Install Dependencies
         if: matrix.runner == 'macos-15'