Use stdint types to define SIZEOF and ALIGNMENT of INTx/WORDx

Authored by wereHamster on Apr 18 2016, 3:11 PM.

Description

Use stdint types to define SIZEOF and ALIGNMENT of INTx/WORDx

Saves us a CPP #if in MachDeps.h since we now can always rely on a
64-bit type being available.

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: thomie, erikd

Differential Revision: https://phabricator.haskell.org/D2099