Bug report

Bug description:

Due to the addition of -Wimplicit-fallthrough as a BASEFLAG new warnings are generated.

This should be reverted until tooling is created to track these new warnings per #112301

Warnings can be found in builds https://buildbot.python.org/all/#/builders/721/builds/1465/steps/3/logs/warnings__143_ from #121030

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-121040: Remove fallthrough warnings compiler option #121041
• gh-121040: Use __attribute__((fallthrough)) #121044