apps/lib/http_server.c needs to include string.h in order to get a prototype
for strerror().
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/11797)
Also adds apps/include/http_server.h.
This is used so far by apps/ocsp.c and is going to be used for apps/cmp.c
and will be helpful also for any future app acting as HTTP server.
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11736)
