It looks like rules_go doesn't account for .dylib files:

https://github.com/bazelbuild/rules_go/blob/7a6f32812eaf167c03ba50fcf75a2750efda1fb3/go/private/actions/link.bzl#L85

Additionally, I believe macOS will need further adjustment when Bazel 0.12 is released, due to this change: bazelbuild/bazel@f98a7a2