Flag --incompatible_config_setting_private_default_visibility will break FlatBuffers in a future Bazel release

[keertk]

Incompatible flag --incompatible_config_setting_private_default_visibility will be enabled by default in a future Bazel release [1], thus breaking FlatBuffers.

The flag is documented here: https://github.com/bazelbuild/bazel/issues/12933.

Please check the following CI builds for build and test results:

• MacOS, OpenJDK 11
• Ubuntu 18.04, OpenJDK 11
• Ubuntu 20.04, OpenJDK 11

Never heard of incompatible flags before? We have documentation that explains everything. If you have any questions, please file an issue in https://github.com/bazelbuild/continuous-integration.

[1] The target release hasn't been determined yet. Our tool will update the issue title once the flag flip has been scheduled.