patch 8.1.1533: GUI build fails on Mac

Problem:    GUI build fails on Mac.
Solution:   Change VimClipboard type in non-C file.
diff --git a/src/os_macosx.m b/src/os_macosx.m
index 3b5c35a..4c04395 100644
--- a/src/os_macosx.m
+++ b/src/os_macosx.m
@@ -40,13 +40,13 @@
 NSString *VimPboardType = @"VimPboardType";
 
     void
-clip_mch_lose_selection(VimClipboard *cbd UNUSED)
+clip_mch_lose_selection(Clipboard_T *cbd UNUSED)
 {
 }
 
 
     int
-clip_mch_own_selection(VimClipboard *cbd UNUSED)
+clip_mch_own_selection(Clipboard_T *cbd UNUSED)
 {
     /* This is called whenever there is a new selection and 'guioptions'
      * contains the "a" flag (automatically copy selection).  Return TRUE, else
@@ -58,7 +58,7 @@
 
 
     void
-clip_mch_request_selection(VimClipboard *cbd)
+clip_mch_request_selection(Clipboard_T *cbd)
 {
     NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
 
@@ -148,7 +148,7 @@
  * Send the current selection to the clipboard.
  */
     void
-clip_mch_set_selection(VimClipboard *cbd)
+clip_mch_set_selection(Clipboard_T *cbd)
 {
     NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];