On rare occasion 's_server | perl -ne print' can complete before
corresponding waitpid, which on Windows can results in -1 return
value. This is not an error, don't treat it like one. Collect
even return value from s_server.
Reviewed-by: NBernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5907)