Thanks to Kannan from Facebook's dev team the patch for OS X is now a part of the official release.
Go get it Mac users! It compiles on OS X perfectly.
Two weeks ago I wrote that I've made a patch for version 0.9.1 to build under OS X.
Then I decided to post a request on XHProf's bug track and supply the patch there.
Kannan (leader of the project) answered and we collaborated in the next week for applying the patch in the next official release of XHProf.
You can read more about the whole story on PECL.
Thank you, Kannan, for your time and efforts!
I am glad that version 0.9.2 has a port for Mac OS X and I was able to help for that.