Summary:
This is a hack for now to allow fbsource-based watchman getdeps builds to
succeed.  In the long run we need to update Watchman's CMakeLists.txt to
depend on a proper EdenFS build, rather than copying Eden's thrift files into
Watchman's source tree.

Reviewed By: wez

Differential Revision: D15753320

fbshipit-source-id: 2dea483c2053c4ea1cf64021c4bbc3239fce645d