patch 8.2.0907: when using :global clipboard isn't set correctly

Problem:    When using :global clipboard isn't set correctly.
Solution:   Set "clip_unnamed_saved" instead of "clip_unnamed". (Christian
            Brabandt, closes #6203, closes #6198)

src/clipboard.c

@@ -1317,7 +1317,12 @@ check_clipboard_option(void)
     }
     if (errmsg == NULL)
     {
-	clip_unnamed = new_unnamed;
+	if (global_busy)
+	    // clip_unnamed will be reset to clip_unnamed_saved
+	    // at end_global_changes
+	    clip_unnamed_saved = new_unnamed;
+	else
+	    clip_unnamed = new_unnamed;
 	clip_autoselect_star = new_autoselect_star;
 	clip_autoselect_plus = new_autoselect_plus;
 	clip_autoselectml = new_autoselectml;

src/testdir/test_global.vim

@@ -1,3 +1,4 @@
+source check.vim
 
 func Test_yank_put_clipboard()
   new
@@ -13,6 +14,16 @@ func Test_yank_put_clipboard()
   bwipe!
 endfunc
 
+func Test_global_set_clipboard()
+  CheckFeature clipboard_working
+  new
+  set clipboard=unnamedplus
+  let @+='clipboard' | g/^/set cb= | let @" = 'unnamed' | put
+  call assert_equal(['','unnamed'], getline(1, '$'))
+  set clipboard&
+  bwipe!
+endfunc
+
 func Test_nested_global()
   new
   call setline(1, ['nothing', 'found', 'found bad', 'bad'])

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    907,
 /**/
     906,
 /**/