bpo-40503: Add compile-time configuration to PEP 615 by pganssle · Pull Request #20034 · python/cpython

The import machinery can be somewhat fragile, and the "seamlessly falls
back to pure Python" nature of this module makes it so that a problem
building the C extension or a failure to import the pure Python version
might easily go unnoticed.

This adds some "smoke tests" that rely on implementation details of each
module to ensure that we're building the ones we think we are.

This should improve support on Windows, including actually building the C
extension.

Suggestion by Petr Viktorin.

This is configurable only on POSIX systems at the moment and TZPATH is
initialized to an empty string on Windows.