Building extensions with hardening flags (via manylinux)

Posting here at the request of @mayeut to get a broader audience. The Fedora project aims to enable user-level support for x86_64 shadow stacks in the Fedora Linux 46 release, which is scheduled for spring 2027. The effort is being coordinated by @submachine; technical details can be found in the Fedora change proposal. This will affect Python in the following way. A multi-threaded process that runs with the shadow-stack feature on will refuse to dlopen() a shared library that was built witho...