Fix wheel builds on musllinux_1_2 containers

[nitzmahone]

The static wheel extension build is broken again under musllinux_1_2 - need to find a more stable configuration to smuggle through the right config to setuptools to ignore the packaged libffi headers/libs and always favor the one we built. Alpine makes that a bit of an extra challenge, since we can't reliably just remove the packaged ones without breaking busybox (and other tools), and its script-based ldconfig isn't usually capable enough to do what we need.

[nitzmahone]

(we're currently forcing wheel builds to use musllinux_1_1)