There is now a proposed patch on issue23042 which, having gone through those changes, may well address this issue too.

Testing that patch on multiple platforms (including the RHEL variants relevant here) would be much appreciated.

Thanks goes to @lemburg for doing the investigative work and providing the diffs that occurred to the Modules/_ctypes/libffi/src/x86/ffi.c file in the past -- that work made the patch possible to sort out.