Michal Terepeta authored Jul 20, 2015 and Ben Gamari committed Jul 20, 2015

This adds support MO_U_Mul2 to the LLVM backend by simply using 'mul'
instruction but operating at twice the bit width (e.g., for 64 bit
words we will generate mul that operates on 128 bits and then extract
the two 64 bit values for the result of the CallishMachOp).

Test Plan: validate

Reviewers: rwbarton, austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1068

GHC Trac Issues: #9430