o_time.c: use gmtime_s with MSVC

ts/ts_rsp_sign.c: change to OPENSSL_gmtime.

Reviewed-by: Andy Polyakov <appro@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5720)

(cherry picked from commit 98c03302)