Make tests and examples use glad

tests/joysticks.c

@@ -28,6 +28,7 @@
 //
 //========================================================================
 
+#include <glad/glad.h>
 #include <GLFW/glfw3.h>
 
 #include <stdio.h>
@@ -216,6 +217,7 @@ int main(void)
     glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
 
     glfwMakeContextCurrent(window);
+    gladLoadGLLoader((GLADloadproc) glfwGetProcAddress);
     glfwSwapInterval(1);
 
     while (!glfwWindowShouldClose(window))