Fixed RenderDoc define on Linux.

3rdparty/renderdoc/renderdoc_app.h

@@ -36,7 +36,7 @@
 #endif
 #define RENDERDOC_CC __cdecl
 
-#elif defined(LINUX)
+#elif defined(__linux__)
 
 #ifdef RENDERDOC_EXPORTS
 #define RENDERDOC_API __attribute__ ((visibility ("default")))