Add a micro-test for the transforms I added to JumpThreading.

I have not been able to find a way to test each in isolation, for a few reasons:
1) The ability to look-through non-i1 BinaryOperator's requires the ability to look through non-constant
   ICmps in order for it to ever trigger.
2) The ability to do LVI-powered PHI value determination only matters in cases that ProcessBranchOnPHI
   can't handle.  Since it already handles all the cases without other instructions in the def-use chain
   between the PHI and the branch, it requires the ability to look through ICmps and/or BinaryOperators
   as well.

llvm-svn: 112611