[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 This fixes an assertion when building the emulators/snes9x port. Reported by: jbeich PR: 225471 MFC after: 3 months X-MFC-With: r327952