avoid build breakage on lame pseudo-OS that cannot unlink open file

Delivery of image theme zip can fail when a unit test runs concurrently
and has the zip file opened on WNT.  Horrible hack to have vcl depend on
the image themes should prevent that.

Change-Id: I4b65dbb6cae8738d52153eba3397b17e94cdc7c9

vcl/Library_vcl.mk

@@ -675,4 +675,8 @@ endif
 # Runtime dependency for unit-tests
 $(eval $(call gb_Library_use_restarget,vcl,vcl))
 
+# HACK: dependency on icon themes so running unit tests don't
+# prevent delivering these by having open file handles on WNT
+$(eval $(call gb_Library_use_package,vcl,postprocess_images))
+
 # vim: set noet sw=4 ts=4: