patch 8.1.2192: cannot easily fill the info popup asynchronously

Problem:    Cannot easily fill the info popup asynchronously.
Solution:   Add the "popuphidden" value to 'completeopt'. (closes #4924)
diff --git a/src/proto/popupwin.pro b/src/proto/popupwin.pro
index d6ba3e7..4ec4a74 100644
--- a/src/proto/popupwin.pro
+++ b/src/proto/popupwin.pro
@@ -26,6 +26,7 @@
 void f_popup_menu(typval_T *argvars, typval_T *rettv);
 void f_popup_notification(typval_T *argvars, typval_T *rettv);
 void f_popup_close(typval_T *argvars, typval_T *rettv);
+void popup_hide(win_T *wp);
 void f_popup_hide(typval_T *argvars, typval_T *rettv);
 void popup_show(win_T *wp);
 void f_popup_show(typval_T *argvars, typval_T *rettv);