ci: Download clang/lldb from tarballs

Hopefully will speed up CI slightly!

src/ci/init_repo.sh

@@ -55,6 +55,7 @@ function fetch_submodule {
 }
 
 included="src/llvm src/llvm-emscripten src/doc/book src/doc/rust-by-example"
+included="$included src/tools/lld src/tools/clang src/tools/lldb"
 modules="$(git config --file .gitmodules --get-regexp '\.path$' | cut -d' ' -f2)"
 modules=($modules)
 use_git=""