tools: add missing #include "unicode/putil.h"

* we use u_setDataDirectory() in "unicode/putil.h"
* at present, this header is indirectly included,
  but this will change in ICU 59
* no impact on past ICUs.
* this is an exact analog to https://github.com/nodejs/node/issues/11753

PR-URL: https://github.com/nodejs/node/pull/12078


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>