add comment about -fno-objc-msgsend-selector-stubs

Author: jbatez

compiler/rustc_codegen_llvm/src/consts.rs

@@ -658,6 +658,10 @@ impl<'ll> CodegenCx<'ll, '_> {
     // deduplicate references within a CGU, but we need a reference definition in each referencing
     // CGU. All attempts at using external references to a single reference definition result in
     // linker errors.
+    //
+    // Newer versions of Apple Clang generate calls to `@"objc_msgSend$methname"` selector stub
+    // functions. We don't currently do that. The code we generate is closer to what Apple Clang
+    // generates with the `-fno-objc-msgsend-selector-stubs` option.
     fn get_objc_selref(&self, methname: Symbol) -> &'ll Value {
         let mut selrefs = self.objc_selrefs.borrow_mut();
         if let Some(selref) = selrefs.get(&methname).copied() {