Erik de Castro Lopo authored May 12, 2016 and Ben Gamari committed May 12, 2016

Functions like `stgMallocBytes` take a size parameter which was of type
`int`, but is commonly used as `stgMallocBytes (sizeof (...))`. This is
problematic because the `sizeof` operator returns `size_t` so that on 64
bit systems, in this common use case the `size_t` parameter would be
truncated to 32 bits when passed to `stgMallocBytes` where it was cast
back to `size_t`.

Test Plan: Validate on Linux, OS X and Windows

Reviewers: austin, hvr, bgamari, simonmar, hsyl20

Reviewed By: hvr, bgamari, simonmar, hsyl20

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2201