The function has been removed from openssl 3. Annoyingly enough the
build of serf doesn't fail even with this function being undefined, it
is just reported as a warning:
buckets/ssl_buckets.c:1329:24: warning: implicit declaration of function 'ERR_GET_FUNC' is invalid in C99 [-Wimplicit-function-declaration]
ERR_GET_FUNC(err),
^
but trying to use any program linked against libserf.so later fails.
