libcffi pointers become stale in image save/restore cycle

[Jason Ruchti]

CFFI version: >v0.16.1
Lisp version: SBCL 2.1.5, CCL 1.12
Operating System version: Ubuntu 20.04

This issue is also documented in the code at https://github.com/cffi/cffi/blob/master/libffi/funcall.lisp#L92.

If a cffi function is called prior to image save, the cffi-cache will be populated with pointers to foreign memory. These pointers are serialized to disk as part of the image save process and are stale upon restart of the image, leading to hard errors if the same functions are called in the program.

Would it be possible to store these foreign pointers in a global variable such that it could be cleared in an image dump hook? Thanks.

Related to 366c7369962bddab7c7960489cfd24eeae707817