Fixed SDL platform layer to be separate from Windows platform layer

code/sdl_platform.cpp

@@ -8,7 +8,7 @@
 #include <errno.h>
 #include <dlfcn.h>
 
-#include "platform.h"
+#include "sdl_platform.h"
 
 const char *WindowTitle = "Ray Tracing in a Weekend";
 

code/sdl_platform.h

@@ -1,5 +1,5 @@
-#ifndef PLATFORM_H
-#define PLATFORM_H
+#ifndef SDL_PLATFORM_H
+#define SDL_PLATFORM_H
 
 typedef void plugin_update_and_render(plugin_offscreen_buffer *Buffer);