Merge r1673455 from trunk:

mod_ssl: Protect ENGINE_CTRL_CHIL_SET_FORKCHECK macro with a 
featue check for libressl.

Submitted by: Stuart Henderson <sthen openbsd.org>
Reviewed by: covener, trawick, ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1673900 13f79535-47bb-0310-9956-ffa450edef68