Per discussion in https://github.com/envoyproxy/envoy/pull/5875#discussion_r256319464, local Bazel builds with `--config libc++` are broken since https://github.com/envoyproxy/envoy/pull/5875, though they seem to work fine on the CI. cc @htuch @lizan