glx: Guard some of the bind_extensions() code with the same conditions as glx_screens frontend_screen member.

Configution like simple MacOS builds do not have `frontend_screen` and fail to build.

Fixes: 34dea2b38e ("glx: unify extension binding")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/12317

Tested-by: Yurii Kolesnykov <root@yurikoles.com>
(cherry picked from commit 48ebbe2777)

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33113>

.pick_status.json

@@ -674,7 +674,7 @@
         "description": "glx: Guard some of the bind_extensions() code with the same conditions as `glx_screen`s `frontend_screen` member.",
         "nominated": true,
         "nomination_type": 2,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "34dea2b38eb336e0414d60b168b9209e029a8cad",
         "notes": null

src/glx/glxext.c

@@ -790,6 +790,7 @@ bind_extensions(struct glx_screen *psc, const char *driverName)
       __glXEnableDirectExtension(psc, "GLX_INTEL_swap_event");
    }
 
+#if defined(GLX_DIRECT_RENDERING) && (!defined(GLX_USE_APPLEGL) || defined(GLX_USE_APPLE))
    mask = driGetAPIMask(psc->frontend_screen);
 
    __glXEnableDirectExtension(psc, "GLX_ARB_create_context");
@@ -846,6 +847,7 @@ bind_extensions(struct glx_screen *psc, const char *driverName)
          psc->keep_native_window_glx_drawable = keep_native_window_glx_drawable;
       }
    }
+#endif
 }