Add gl_set_proc_address to both sdl2 and glfw as utility loaders for OpenGL

vendor/glfw/wrapper.odin

@@ -222,4 +222,10 @@ SetCharModsCallback    :: glfw.SetCharModsCallback;
 SetCursorEnterCallback :: glfw.SetCursorEnterCallback;
 SetJoystickCallback    :: glfw.SetJoystickCallback;
 
-SetErrorCallback :: glfw.SetErrorCallback;
+SetErrorCallback :: glfw.SetErrorCallback;
+
+
+// Used by vendor:OpenGL
+gl_set_proc_address :: proc(p: rawptr, name: cstring) {
+	(^rawptr)(p)^ = GetProcAddress(name);
+}