Link std_image statically.

code/Pbrt/PbrtExporter.cpp

@@ -83,7 +83,16 @@ Other:
 #include <sstream>
 #include <string>
 
+#if _MSC_VER // "unreferenced function has been removed" (SSE2 detection routine in x64 builds)
+#pragma warning(push)
+#pragma warning(disable : 4505)
+#endif
+#define STB_IMAGE_STATIC
+#define STB_IMAGE_IMPLEMENTATION
 #include "stb/stb_image.h"
+#if _MSC_VER
+#pragma warning(pop)
+#endif
 
 using namespace Assimp;