Add attribute to check if return value of certain functions is incorrectly
ignored.
diff --git a/e_os2.h b/e_os2.h
index 4c785c6..f5a5fa2 100644
--- a/e_os2.h
+++ b/e_os2.h
@@ -283,6 +283,12 @@
 # define OPENSSL_GLOBAL_REF(name) _shadow_##name
 #endif
 
+#ifdef DEBUG_UNUSED
+#define __owur __attribute__((__warn_unused_result__))
+#else
+#define __owur 
+#endif
+
 #ifdef  __cplusplus
 }
 #endif