Fixed a -Wundef warning in cl_platform.h.

_MSC_VER -> defined _MSC_VER. Fixes building with MinGW.
Similar to fbc91c5e.

3rdparty/include/opencl/1.2/CL/cl_platform.h

@@ -454,7 +454,7 @@ typedef unsigned int cl_GLenum;
 /* Define alignment keys */
 #if defined( __GNUC__ )
     #define CL_ALIGNED(_x)          __attribute__ ((aligned(_x)))
-#elif defined( _WIN32) && (_MSC_VER)
+#elif defined( _WIN32) && defined(_MSC_VER)
     /* Alignment keys neutered on windows because MSVC can't swallow function arguments with alignment requirements     */
     /* http://msdn.microsoft.com/en-us/library/373ak2y1%28VS.71%29.aspx                                                 */
     /* #include <crtdefs.h>                                                                                             */