Correct limb length and assertion for gcdExtInteger

Authored by DavidEichamnn <EichmannD@gmail.com> on Aug 21 2018, 3:06 PM.

Description

Correct limb length and assertion for gcdExtInteger

Reviewers: hvr, bgamari, monoidal

Reviewed By: monoidal

Subscribers: monoidal, rwbarton, thomie, carter

GHC Trac Issues: Trac #15350

Differential Revision: https://phabricator.haskell.org/D5042

(cherry picked from commit c331592130ef592b92084e7417581a4039bfa7d2)