Try out clang-tidy using clang-cl on Windows

As of r279120, clang-tidy should be working on Windows with the clang-cl driver. The standard instructions for configuring and using clang-tidy apply and there are no differences for Windows.

Let me know if you run into any issues. I’m looking into how difficult it will be to update the vs plugin to support clang-tidy. So look for that on the horizon too.