Cycles: Fix compilation error after recent logging changes

Forbid OSL from polluting current conext with obscure stuff from
windows.h, it's not useful and unhealthy anyway.

Maybe we sohuld also forbid using abbreviated Glog constants as
well tho.

intern/cycles/render/shader.h

@@ -18,6 +18,15 @@
 #define __SHADER_H__
 
 #ifdef WITH_OSL
+#  if defined(_MSC_VER)
+/* Prevent OSL from pollyting the context with weird macroses from windows.h.
+ * TODO(sergey): Ideally it's only enough to have class/struct declarations in
+ * the header and skip header include here.
+ */
+#    define NOGDI
+#    define NOMINMAX
+#    define WIN32_LEAN_AND_MEAN
+#  endif
 #  include <OSL/oslexec.h>
 #endif