Merge r1702948, r1759415 from trunk:

httpd compiles warning free on gcc and every new warning will be treated as an error, standard c-89 is enforced

http_config: follow up to r1702948: maybe unused, yet maybe usefull too.
Submitted by: icing, ylavic
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1772330 13f79535-47bb-0310-9956-ffa450edef68