[ConstantFolding, InstSimplify] Handle more vector GEPs

This patch addresses some additional cases where the compiler crashes upon
encountering vector GEPs. This should fix PR36116.

Differential Revision: https://reviews.llvm.org/D44219
Reference: https://bugs.llvm.org/show_bug.cgi?id=36116

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327638 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed