Fix XHP build on gcc 4.1
Fix XHP build on gcc 4.1

Summary:
There is an undefined function that I don't even know how it gets defined, but it does in gcc > 4.1. Collocating this function in ext.cpp so older versions of gcc can build XHP.

Reviewed By: dweatherford

Test Plan:
Build using gcc 4.1.2 and php 5.3.2

facebook/xhp-lib