remove any conditional source file inclusion in the CMake build
remove any conditional source file inclusion in the CMake build

Summary:
Our coding convention encourages us to put ifdefs inside source files
and headers, and unconditionally include them. Remove the last
win32-specific source files from the CMake build.

Reviewed By: genevievehelsel

Differential Revision: D36337280

fbshipit-source-id: b398907510bb2a2e8d7c1307d224cebd63d12469

facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman