Fix evaluator for non-zero alloca addr space

The evaluator goes through BB and creates global vars as temporary values to evaluate
results of LLVM instructions. It creates undef for alloca, however it assumes alloca
in addr space 0. If the next instruction is addrspace cast to 0, then we get an invalid
cast instruction.

This patch let the temp global var have an address space matching alloca addr space,
so that the valuation can be done.

Differential Revision: https://reviews.llvm.org/D47081

llvm-svn: 332794