tests CHANGE wrapping functions on OSX

OSX's linker does not support --wrap option to wrap a function. We use
it for testing, so disable such tests on OSX.
diff --git a/src/config.h.in b/src/config.h.in
index 2a2af23..0d9284b 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -15,6 +15,8 @@
 #ifndef LY_CONFIG_H_
 #define LY_CONFIG_H_
 
+#cmakedefine APPLE
+
 /**
  * @brief Compiler flag for unused function attributes
  */