so apparently it's possible to compile PHP do decouple it from the interpreter:
http://en.wikipedia.org/wiki/Php#Compilers
but then once you do so, how would you configure apache so that it'll be able to serve websites using the compiled PHP instead of interpreted PHP?
https://github.com/facebook/hiphop-php/wiki/Running-HipHop
You have an example here on how to compile WordPress and how to run it.
However, for smaller projects it's much better to use APC. It provides extreme speed gain - not as much as hiphop, but you can still use Apache, eval() and run standard php configuration.