package/pound: Fix build with OpenSSL 1.1.x

package/pound: Fix build with OpenSSL 1.1.x

The patches enable two new API configurations, one for OpenSSL 1.1.x
and the other LibreSSL.

A dependency is added to use the Buildroot host tool openssl to
create headers (dh512.h).  This resolves a host OS mismatch with
openssl versions. (The Makefile does this generation as part of
the initial build)

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Patrick Havelange <patrick.havelange@essensium.com>
Signed-off-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>