[InstSimplify] fold funnel shifts with undef operands

Splitting these off from the D54666.

Patch by: nikic (Nikita Popov)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@347332 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed