Add entry point into gents.
Add entry point into gents.

Summary:
This adds another entry point into the gradle build to
generate an executable for gents in addition to clutz.

Reviewers: mprobst, rkirov, alexeagle

Reviewed By: rkirov, alexeagle

Subscribers: alexeagle, typescript-eng

Differential Revision: https://reviews.angular.io/D190

rehmsen/clutz,dpurp/clutz,polybuildr/clutz,angular/clutz,dpurp/clutz,angular/clutz,polybuildr/clutz,dpurp/clutz,rehmsen/clutz,rehmsen/clutz,angular/clutz,polybuildr/clutz