patch 8.2.0320: no Haiku support

Problem:    No Haiku support.
Solution:   Add support for Haiku. (Emir Sari, closes #5605)
diff --git a/src/mbyte.c b/src/mbyte.c
index abb07ae..802df49 100644
--- a/src/mbyte.c
+++ b/src/mbyte.c
@@ -6488,7 +6488,7 @@
 #  endif
 }
 
-#  if defined(FEAT_GUI) && !defined(VIMDLL)
+#  if defined(FEAT_GUI) && !defined(FEAT_GUI_HAIKU) && !defined(VIMDLL)
     void
 im_set_position(int row UNUSED, int col UNUSED)
 {