Test for the the problem with xors being changed into ands

when the set bits aren't the same for both args of the xor.
This transformation is in the function TargetLowering::SimplifyDemandedBits
in the file lib/CodeGen/SelectionDAG/TargetLowering.cpp.

I have tested this test using a previous version of llc which the defect and 
the a version of llc which does not. I got the expected fail and pass, 
respectively.

This test goes with rdar://11195364 and the check in with the fix: svn r154955

llvm-svn: 155156