Add clang-cl support

[robertodr]

• Set up Azure pipeline to test clang-cl
• Fix various CMakeLists.txt for new compiler.

This is the Azure build log You'll need an Azure free account and set up pipelines to actually use the YAML file.

The testing step currently fails with:

Fatal Python error: Py_Initialize: unable to load the file system codec
ModuleNotFoundError: No module named 'encodings'

I think this means conflicting versions of Python are present. I am working on fixing this.