patch 8.1.1531: clipboard type name is inconsistent

Problem:    Clipboard type name is inconsistent.
Solution:   Rename VimClipboard to Clipboard_T.
diff --git a/src/gui_x11.c b/src/gui_x11.c
index edf69dd..3555ffa 100644
--- a/src/gui_x11.c
+++ b/src/gui_x11.c
@@ -2872,26 +2872,26 @@
  */
 
     void
-clip_mch_lose_selection(VimClipboard *cbd)
+clip_mch_lose_selection(Clipboard_T *cbd)
 {
     clip_x11_lose_selection(vimShell, cbd);
 }
 
     int
-clip_mch_own_selection(VimClipboard *cbd)
+clip_mch_own_selection(Clipboard_T *cbd)
 {
     return clip_x11_own_selection(vimShell, cbd);
 }
 
     void
-clip_mch_request_selection(VimClipboard *cbd)
+clip_mch_request_selection(Clipboard_T *cbd)
 {
  clip_x11_request_selection(vimShell, gui.dpy, cbd);
 }
 
     void
 clip_mch_set_selection(
-    VimClipboard	*cbd)
+    Clipboard_T	*cbd)
 {
     clip_x11_set_selection(cbd);
 }