sysutils/aimage: Unbreak build with Clang 6
- Also fix build with LibreSSL: The configure script checks that libssl has ssl3_new() which LibreSSL doesn't have but aimage itself never uses it, so pretend it's there to pass the check.
PR: 228756
Reported by: Chris Hutchinson <portmaster@bsdforge.com>
Submitted by: tobik
Approved by: Chris Hutchinson <portmaster@bsdforge.com> (maintainer)