Fix invalid shufflevector operands

This patch fixes bug 23800 ( https://llvm.org/bugs/show_bug.cgi?id=23800#c2 ). There existed a case where the index operand from extractelement was directly used to create a shufflevector mask. Since the index can be of any integral type but the mask must only contain 32 bit integers a 64 bit index operand led to an assertion error later on.

Committed on behalf of mpflanzer (Moritz Pflanzer)

Differential Revision: http://reviews.llvm.org/D10838

llvm-svn: 243851