[CodeGen] Fix result type for SMULO/UMULO legalization

On some platforms (like MSP430) the second element of the result
structure for SMULO/UMULO may have a shorter type than the one
returned by SetCC. We need to truncate it to the right type, or
else some incorrect code may be generated later on.

This fixes issue rust-lang/rust#37829

Patch by Vadzim Dambrouski!

Differential Revision: https://reviews.llvm.org/D27154

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@288857 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Eli Friedman