Summary:
D19222635 added a `ReentrantAllocatorTest.cpp` test file but in the
CMakeLists.txt file it listed `MmapAllocatorTest.cpp` instead.

Reviewed By: yfeldblum

Differential Revision: D19650216

fbshipit-source-id: 794ced255de6781a05da7114eb7f8b3258f90a8c