geniconv/os2iconv.c: make it build correctly against os2tk headers.
diff --git a/src/core/os2/geniconv/os2iconv.c b/src/core/os2/geniconv/os2iconv.c
index 617a355..d7dfe06 100644
--- a/src/core/os2/geniconv/os2iconv.c
+++ b/src/core/os2/geniconv/os2iconv.c
@@ -28,6 +28,8 @@
#define ICONV_THREAD_SAFE 1
#include "geniconv.h"
+#define _ULS_CALLCONV_
+#define CALLCONV _System
#include <uconv.h>
#include <stdio.h>
#include <stdlib.h>