EGL: Ensure the platform extensions exist before using them

The EXT and KHR variants use the same constant values, but the EXT versions are available a bit further back.

src/video/wayland/SDL_waylandopengles.c

@@ -37,10 +37,15 @@
 
 int Wayland_GLES_LoadLibrary(_THIS, const char *path)
 {
-    int ret;
     SDL_VideoData *data = (SDL_VideoData *)_this->driverdata;
+    int ret;
+#ifdef EGL_EXT_platform_wayland
+    const EGLenum platform = EGL_PLATFORM_WAYLAND_EXT;
+#else
+    const EGLenum platform = 0;
+#endif
 
-    ret = SDL_EGL_LoadLibrary(_this, path, (NativeDisplayType) data->display, EGL_PLATFORM_WAYLAND_KHR);
+    ret = SDL_EGL_LoadLibrary(_this, path, (NativeDisplayType) data->display, platform);
 
     Wayland_PumpEvents(_this);
     WAYLAND_wl_display_flush(data->display);

src/video/x11/SDL_x11opengles.c

@@ -32,6 +32,11 @@
 int X11_GLES_LoadLibrary(_THIS, const char *path)
 {
     SDL_VideoData *data = (SDL_VideoData *)_this->driverdata;
+#ifdef EGL_EXT_platform_x11
+    const EGLenum platform = EGL_PLATFORM_X11_EXT;
+#else
+    const EGLenum platform = 0;
+#endif
 
     /* If the profile requested is not GL ES, switch over to X11_GL functions  */
     if ((_this->gl_config.profile_mask != SDL_GL_CONTEXT_PROFILE_ES) &&
@@ -53,8 +58,7 @@ int X11_GLES_LoadLibrary(_THIS, const char *path)
 #endif
     }
 
-    return SDL_EGL_LoadLibrary(_this, path, (NativeDisplayType) data->display,
-                               EGL_PLATFORM_X11_KHR);
+    return SDL_EGL_LoadLibrary(_this, path, (NativeDisplayType) data->display, platform);
 }
 
 XVisualInfo *X11_GLES_GetVisual(_THIS, Display *display, int screen)