Flag --incompatible_no_implicit_file_export will break Bazel toolchains in Bazel 1.2.1

[bazel-flag-bot]

Incompatible flag --incompatible_no_implicit_file_export will break Bazel toolchains once Bazel 1.2.1 is released.

Please see the following CI builds for more information:

• [RBE (:ubuntu: 16.04, OpenJDK 8)](RBE (:ubuntu: 16.04, OpenJDK 8))
• [RBE (:ubuntu: 16.04, OpenJDK 8)](RBE (:ubuntu: 16.04, OpenJDK 8))

Questions? Please file an issue in https://github.com/bazelbuild/continuous-integration

Important: Please do NOT modify the issue title since that might break our tools.