Fix build errors when Xcode 12 is used.

src/libraries/glad/glad.cpp

@@ -1,8 +1,4 @@
 #include <string.h>
-#include "glad.hpp"
-
-namespace glad {
-
 
 #ifdef GLAD_USE_SDL
 #include <SDL.h>
@@ -13,6 +9,10 @@ namespace glad {
 #include <assert.h>
 #endif
 
+#include "glad.hpp"
+
+namespace glad {
+
 bool gladLoadGL(void) {
 #ifdef GLAD_USE_SDL
     return gladLoadGLLoader(SDL_GL_GetProcAddress);