Class statfs

flow/Platform.actor.cpp:600–600

	uint64_t blockSize = buf.f_frsize;
#elif defined(__APPLE__)
	struct statfs buf;
	if (statfs(directory.c_str(), &buf)) {
		Error e = systemErrorCodeToError();
		TraceEvent(SevError, "GetDiskBytesStatfsError").error(e).detail("Directory", directory).GetLastError();