/* MSVC 2015 needs this ugly hack to prevent a codegen bug on x86
* see T50176 for details
*/
-#if _MSC_VER==1900
-# define MSVC_VOLATILE volatile
+#if defined(_MSC_VER) && (_MSC_VER == 1900)
+# define MSVC_VOLATILE volatile
#else
-# define MSVC_VOLATILE
+# define MSVC_VOLATILE
#endif
/* Paper used: Importance Sampling Microfacet-Based BSDFs with the