patch 8.1.1391: no popup window support

Problem:    No popup window support.
Solution:   Add initial code for popup windows.  Add the 'wincolor' option.
diff --git a/src/option.h b/src/option.h
index 082ff9b..7e657dd 100644
--- a/src/option.h
+++ b/src/option.h
@@ -1116,6 +1116,7 @@
     , WV_BRI
     , WV_BRIOPT
 #endif
+    , WV_WCR
 #ifdef FEAT_DIFF
     , WV_DIFF
 #endif