patch 8.2.1898: command modifier parsing always uses global cmdmod

Problem:    Command modifier parsing always uses global cmdmod.
Solution:   Pass in cmdmod_T to use.  Rename struct fields consistently.
diff --git a/src/gui_gtk_x11.c b/src/gui_gtk_x11.c
index e90bdba..2c5864e 100644
--- a/src/gui_gtk_x11.c
+++ b/src/gui_gtk_x11.c
@@ -2226,10 +2226,10 @@
     save_cmdmod = cmdmod;
 
 # ifdef FEAT_BROWSE
-    cmdmod.browse = TRUE;
+    cmdmod.cmod_flags |= CMOD_BROWSE;
 # endif
 # if defined(FEAT_GUI_DIALOG) || defined(FEAT_CON_DIALOG)
-    cmdmod.confirm = TRUE;
+    cmdmod.cmod_flags |= CMOD_CONFIRM;
 # endif
     /*
      * If there are changed buffers, present the user with