Disable -Wtautological-compare for INTEGER_TO_PY() calls for clang.

Without this, INTEGER_TO_PY() produces clang errrors like this on some
platforms:

  _helpers.c:1019:41: error: comparison of unsigned expression >= 0 is always true
  [-Werror,-Wtautological-compare]
                           (((st->st_uid) >= 0) ? PyLong_FromUnsignedLongLong(st->st_uid) :
  PyLong_FromLongLong(st->st_uid)),
                             ~~~~~~~~~~~~ ^  ~

Thanks to Greg Troxel <gdt@lexort.com> for the report.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>