There are a few things I missed in gh-27980. This is a follow-up that will make subsequent PRs cleaner. It includes fixes to tests and tools that reference the frozen modules. https://bugs.python.org/issue45019
This directory contains the generated .h files for all the frozen modules. Python/frozen.c depends on these files. Note that, other than the required frozen modules, none of these files are committed into the repo. See Tools/scripts/freeze_modules.py for more info.