Summary: update macro for OFF_T so that sanitizer works on AARCH64.

Reviewers: vitalybuka, eugenis, MaskRay

Reviewed By: eugenis, MaskRay

Subscribers: MaskRay, kristof.beyls, #sanitizers, llvm-commits, jkz, scw

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D72367