Summary:
shiftRightLogical used a host sized Word for the intermediate value,
which would produce the wrong result when cross compiling to a target
with a different word size than the host.

removeOp32 used the preprocessor to bake in word size assumptions,
rather than getting the target word size from DynFlags

Test Plan: validate

Reviewers: hvr, rwbarton, carter, austin

Reviewed By: austin

Subscribers: thomie, carter

Differential Revision: https://phabricator.haskell.org/D502

GHC Trac Issues: #9736