Check for integer overflow in allocate() (#9172)

Summary: Check for integer overflow in allocate() (#9172)

Test Plan: validate

Reviewers: austin

Reviewed By: austin

Subscribers: simonmar, relrod, carter

Differential Revision: https://phabricator.haskell.org/D36

(cherry picked from commit db641808)

Conflicts:
	testsuite/.gitignore