I looked in mpss-3.5/k1om on the off chance that it might already be provided but it is not. I have never seen anyone try building it but even if you can build it, do you think it is a good idea, given that the coprocessor has no disks? You would only want to serve up information you created on the coprocessor so that you are not moving data to the coprocessor only to send it away again.
of course, I just had to try it ;-)
Building Apache HTTPD 2.x requires building Apache APR (and apr-util) first.
Crosscompiling APR for the Xeon Phi actually does not work out of the box, but with a few hacks I now have a working set of libraries and tools. The apr testsuite fails on flock tests but nothing drastically wrong that I could see. Note: the apr_pollset_create test passed!
Next came the pcre library , which httpd also wants. Again, no real problems again.
Finally, build httpd. Building it was OK, running it however, was not: at startup I get an error that apr_pollset_create is not supported on this platform!
Conclusion: building apache for the Xeon Phi is non-trivial but should be possible. I fully agree with Frances, however: what's the usecase?