Windows build broken

[95-martin-orion]

The Windows builds on Kokoro are breaking with a number of disconcerting messages:

> bazel test --test_output=errors --copt=/D_USE_MATH_DEFINES tests:all
ERROR: C:/tools/msys64/home/kbuilder/_bazel_kbuilder/yic25m7j/external/local_config_cc/BUILD:274:24:
unterminated string literal at eol
{...}
Target '//lib:vectorspace' depends on toolchain '@local_config_cc//:cc-compiler-x64_windows',
which cannot be found

These do not appear in previous passing runs. This failure is blocking submit (#521).

[95-martin-orion]

This appears to be the result of changes in the Tensorflow toolchain location - hoping to have a fix out later today.

[95-martin-orion]

This fix has been delayed due to long-standing inconsistencies between the qsim and Tensorflow build processes, which we're now trying to reconcile. Existing builds of qsim (installed with pip install qsimcirq) are unaffected by this, but open PRs will continue to be blocked for a while longer. Thank you for your patience.

[95-martin-orion]

In the absence of a quick solution for this, we have opted to disable the qsim Windows build to unblock other PRs. We will continue working with the TFQ team to resolve the issue, but for the time being Windows users are advised to install the most recent release prior to the issue (qsimcirq==0.12.1).