apache ebuild seems to ignore if one enables the proxy_http module.
This is what the ebuild passes to ./configure:
But according to ./configure --help it must be --enable-proxy-http. This is the same in 2.2, but it seems back then apache configure was more tolerant and worked anyway, which is no longer the case.
I've tested this with apache-2.4.9-r2 and the module was built.
Are you sure this is still an issue?
No, just checked, I can't reproduce it any more right now.
This report is 1,5 years old, probably something changed inbetween that fixed this, I think we can close.