util/mkerr.pl: Add an inclusion of symhacks.h in all error files

This does no harm, and ensures that the inclusion isn't mistakenly
removed in the generated *err.h where it's actually needed.

Reviewed-by: Nicola Tuveri <nic.tuv@gmail.com>
Reviewed-by: Richard Levitte <levitte@openssl.org>

(cherry picked from commit b53c4fe3f92e3d2c5bd9fca1a171cd24f66ef14d)

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/9281)