Missing symbol for Abseil ParseTime Op

[seanpmorgan]

Describe the bug
Since the 20101030 nightly, our library fails when opening the _parse_time_op.so because of an undefined symbol error. Typically this occurs when there is an ABI incompatibility between core TensorFlow and our custom-ops.

tensorflow.python.framework.errors_impl.NotFoundError: .../custom_ops/text/_parse_time_op.so: undefined symbol: _ZN4absl9ParseTimeERKSsS1_PNS_4TimeEPSs

This particular custom-op utilizes absl and the mangled symbol name does not match what our compiled operation thinks it should be. I'm not really sure how this would happen since the rest of the TensorFlow library was compiled with a compatible gcc version.

CC'ing some people who may have insight into how this can happen:
@yifeif @r4nt @perfinion @gunan

I suppose we could make absl a dependency in our TFA build and compile it ourselves but this seems to be going down a bad path.

Failing Log:
https://source.cloud.google.com/results/invocations/a71d103a-ecac-421c-bc53-ef06648fdc9f/targets/tensorflow_addons%2Fubuntu%2Fgpu%2Fpy3%2Fpresubmit/log

[r4nt]

@scentini for whether this might be due to us not exporting all symbols from absl any more

[scentini]

Yep, seems like it is related to f58c9f8, which changes what we export, see bazelbuild/bazel#7362.

The absl symbols probably came from here, and due to f58c9f8 we just don't export the symbol anymore.
I think the right way forward is to make _parse_time_op.so depend on absl.

[seanpmorgan]

Great thanks that makes sense! cc @helinwang as code owner.

Helin if you have time could you submit a patch to add absl as a build dependency.

[scentini]

After discussion with @r4nt, it might be better to not pass the absl dependency to _parse_time_op.so, but rather add alwayslink = 1 to the absl library. (thus make sure that absl symbols are present in @local_config_tf//:libtensorflow_framework)

The reason for this is, if we pass absl as a dependency, we may end up linking global initializers multiple times.

I can send out a fix for this tomorrow.

[helinwang]

Thanks, everyone! If there is anything I can help, please let me know.

[leozwang]

thanks guys! when will the bug-fix be ready? next release or next nightly build?