The `add` and `seed` callbacks were changed to return `int` instead of
`void` in b6dcdbfc94c482f6c15ba725754fc9e827e41851 (first included in
tag OpenSSL_1_1_0-pre1).
Reviewed-by: Matt Caswell <matt@openssl.org> Reviewed-by: Ben Kaduk <kaduk@mit.edu> Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/11486)