Python 3 wheels for Windows x64 aren't getting built

[soltanmm]

And I don't know why the Py3 builds are reported as 'succeeding' anyway on the Windows builders.

Setting for 1.1 as a long-tail target because Python 3 support is still technically in beta, but this issue is receiving immediate attention.

[tseaver]

The 3.4 Windows wheels are also not installable on Python 3.5, leading to gcloud Appveyor errors.

[nathanielmanistaatgoogle]

@kpayson64 spent some time on this in the last week (thanks!).

[nathanielmanistaatgoogle]

@tseaver: I'm not sure I understand your comment - are you saying that there is a circumstance in which you are able to pip install --upgrade --pre grpcio on Windows with Python 3.4 but not (with the same Windows and underlying system) not Python 3.5?

[tseaver]

@nathanielmanistaatgoogle The Appveyor builds succeed for Python 3.4 32-bit, but fail for Python 3.4 64-bit and for both Python 3.5 32-bit and 64-bit: https://ci.appveyor.com/project/dhermes/gcloud-python

[nathanielmanistaatgoogle]

The 3.5 issue may be a separate problem; I've filed issue 7725 for it.

[kpayson64]

This issue was caused by 64 bit Python3.4 not distributing the static libraries needed for mingw linking. I've generated the needed libpython3.4.a library, and uploaded it to gcs in our grpcTesting project. I've also updated the windows worker bootstrap script to copy this file into the Python34 installation directory as needed.

As a side note, we still need Mingw for Python3.4 because the default msvc compiler for 3.4 is still too old for our code.

[kpayson64]

Here is the master build after the host changes:
https://grpc-testing.appspot.com/view/Artifacts/job/gRPC_build_artifacts/architecture=x64,language=python,platform=windows/

[tseaver]

W00t! All green: https://ci.appveyor.com/project/dhermes/gcloud-python/build/1.0.557.master