Fix ConstantFold's folding of icmp instructions to recognize that,
for example, a one-past-the-end pointer from one global variable may
be equal to the base pointer of another global variable.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173995 91177308-0d34-0410-b5e6-96231b3b80d8