Fix "Macro name is a reserved identifier" on OS X

This also more accurately only sets these definitions for MSVC.

test/shared.c

@@ -19,12 +19,14 @@
  * THE SOFTWARE.
  */
 
+#ifdef _MSC_VER
 #if !defined(_CRT_SECURE_NO_WARNINGS)
 #define _CRT_SECURE_NO_WARNINGS
 #endif
 #if !defined(_CRT_SECURE_NO_DEPRECATE)
 #define _CRT_SECURE_NO_DEPRECATE
 #endif
+#endif
 
 #include "shared.h"
 #include <string.h>