Comment on intentional field order

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -1958,6 +1958,9 @@ pub struct OngoingCodegen<B: ExtraBackendMethods> {
     pub backend: B,
     pub crate_info: CrateInfo,
     pub output_filenames: Arc<OutputFilenames>,
+    // Field order below is intended to terminate the coordinator thread before two fields below
+    // drop and prematurely close channels used by coordinator thread. See `Coordinator`'s
+    // `Drop` implementation for more info.
     pub coordinator: Coordinator<B>,
     pub codegen_worker_receive: Receiver<CguMessage>,
     pub shared_emitter_main: SharedEmitterMain,