!! (WIP) how about this?

src/bootstrap/src/core/build_steps/compile.rs

@@ -458,20 +458,13 @@ pub fn std_crates_for_run_make(run: &RunConfig<'_>) -> Vec<String> {
 
 /// Tries to find LLVM's `compiler-rt` source directory, for building `library/profiler_builtins`.
 ///
-/// Normally it lives in the `src/llvm-project` submodule, but if that submodule
-/// is absent and we have downloaded a copy of CI LLVM, then we try to use the
-/// `compiler-rt` sources from there instead, which lets us avoid checking out
-/// the LLVM submodule.
+/// Normally it lives in the `src/llvm-project` submodule, but if we will be using a
+/// downloaded copy of CI LLVM, then we try to use the `compiler-rt` sources from
+/// there instead, which lets us avoid checking out the LLVM submodule.
 fn compiler_rt_for_profiler(builder: &Builder<'_>) -> PathBuf {
-    // If the LLVM submodule is already active, just update it and use that.
-    builder.update_existing_submodule("src/llvm-project");
-    let submodule_compiler_rt = builder.src.join("src/llvm-project/compiler-rt");
-    if submodule_compiler_rt.exists() {
-        return submodule_compiler_rt;
-    }
-
     // Try to use `compiler-rt` sources from downloaded CI LLVM, if possible.
     if builder.config.llvm_from_ci {
+        builder.config.maybe_download_ci_llvm();
         let ci_llvm_compiler_rt = builder.config.ci_llvm_root().join("compiler-rt");
         if ci_llvm_compiler_rt.exists() {
             return ci_llvm_compiler_rt;