Peter Trommler authored Nov 11, 2015 and Ben Gamari committed Nov 11, 2015

Arithmetic right shifts of more than 31 bits set all bits to
the sign bit on PowerPC. iThe assembler does not allow shift
amounts larger than 32 so do an arithemetic right shift of 31
bit instead.

Fixes #10870

Test Plan: validate (especially on powerpc)

Reviewers: austin, erikd, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1459

GHC Trac Issues: #10870