patch 8.2.0622: Haiku: GUI does not compile

Problem:    Haiku: GUI does not compile.
Solution:   Various fixes. (Emir Sari, closes #5961)
diff --git a/src/beval.h b/src/beval.h
index f446200..4332389 100644
--- a/src/beval.h
+++ b/src/beval.h
@@ -79,6 +79,10 @@
 #ifdef FEAT_GUI_MSWIN
     void		*tofree;
 #endif
+#ifdef FEAT_GUI_HAIKU
+    int			x;
+    int			y;
+#endif
 } BalloonEval;
 
 #define EVAL_OFFSET_X 15 // displacement of beval topleft corner from pointer