message: sys/sendfile.h is actually only defined for Linux.
diff: @@ -18,7 +18,7 @@ limitations under the License.
  #include <fcntl.h>
  #include <stdio.h>
  #include <sys/mman.h>
  -#if !defined(__APPLE__)
  +#if defined(__linux__)
  #include <sys/sendfile.h>
  #endif
  #include <sys/stat.h>
  