Declare ozone_platform_gbm when angle doesn't have build

gni/angle.gni

@@ -36,6 +36,7 @@ if (angle_has_build) {
     dcheck_always_on = false
     angle_use_x11 = (is_linux || is_chromeos) && !is_ggp
     use_ozone = false
+    ozone_platform_gbm = false
     use_fuzzing_engine = false
   }
 }