Support getelementptr instructions which use uint's to index into structure

Support getelementptr instructions which use uint's to index into structure
types and can have arbitrary 32- and 64-bit integer types indexing into
sequential types.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12653 91177308-0d34-0410-b5e6-96231b3b80d8