Handle the version_script property.

Doesn't work when depends on arch/target/etc., but good enough for
libdl_android.

Bug: 186650430
Test: Presubmits.
Change-Id: Ib0facb41a89454717c74663e5e078aedd33d1b9c

bp2build/build_conversion.go

@@ -519,9 +519,7 @@ func isZero(value reflect.Value) bool {
 	case reflect.Struct:
 		valueIsZero := true
 		for i := 0; i < value.NumField(); i++ {
-			if value.Field(i).CanSet() {
-				valueIsZero = valueIsZero && isZero(value.Field(i))
-			}
+			valueIsZero = valueIsZero && isZero(value.Field(i))
 		}
 		return valueIsZero
 	case reflect.Ptr: