[libtooling][biniou] fix integers too large for ocaml
[libtooling][biniou] fix integers too large for ocaml

Test Plan:
The compilation of objc models in infer fails without this:

  cd ~/infer
  make -C infer clang

Reviewers: mathieubaudet

Reviewed By: mathieubaudet

Subscribers: martinoluca

Differential Revision: https://phabricator.fb.com/D2360597

Tasks: 7792959

Signature: t1:2360597:1440005090:0f4162ca0d9bf5673878767e409ba12bc46c41c4

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