rustc: Move a comment to the right spot in trans

I believe this comment here is mostly talking about the `ptrcast` function call
below, so move the comment down to that block.

src/librustc_trans/callee.rs

@@ -53,6 +53,11 @@ pub fn get_fn<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
     let sym = tcx.symbol_name(instance);
     debug!("get_fn({:?}: {:?}) => {}", instance, fn_ty, sym);
 
+    // Create a fn pointer with the substituted signature.
+    let fn_ptr_ty = tcx.mk_fn_ptr(common::ty_fn_sig(ccx, fn_ty));
+    let llptrty = type_of::type_of(ccx, fn_ptr_ty);
+
+    let llfn = if let Some(llfn) = declare::get_declared_value(ccx, &sym) {
         // This is subtle and surprising, but sometimes we have to bitcast
         // the resulting fn pointer.  The reason has to do with external
         // functions.  If you have two crates that both bind the same C
@@ -76,12 +81,6 @@ pub fn get_fn<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
         // This can occur on either a crate-local or crate-external
         // reference. It also occurs when testing libcore and in some
         // other weird situations. Annoying.
-
-    // Create a fn pointer with the substituted signature.
-    let fn_ptr_ty = tcx.mk_fn_ptr(common::ty_fn_sig(ccx, fn_ty));
-    let llptrty = type_of::type_of(ccx, fn_ptr_ty);
-
-    let llfn = if let Some(llfn) = declare::get_declared_value(ccx, &sym) {
         if common::val_ty(llfn) != llptrty {
             debug!("get_fn: casting {:?} to {:?}", llfn, llptrty);
             consts::ptrcast(llfn, llptrty)