apps/ocsp.c Use the same HAVE_FORK / NO_FORK as in speed.c

This allows the user to override our defaults if needed, and in a
consistent manner.

Partial fix for #7607

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7624)

(cherry picked from commit ca811248)