sync llvm submodule during config parse

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

src/bootstrap/src/core/config/config.rs

@@ -1574,6 +1574,12 @@ impl Config {
         set(&mut config.print_step_rusage, print_step_rusage);
         config.patch_binaries_for_nix = patch_binaries_for_nix;
 
+        // Initialize the llvm submodule if not initialized already.
+        // This is required to handle download-ci-llvm properly.
+        //
+        // If submodules are disabled, this does nothing.
+        config.update_submodule("src/llvm-project");
+
         config.verbose = cmp::max(config.verbose, flags.verbose as usize);
 
         if let Some(install) = toml.install {