[InstCombine] Add new tests in preparation for a combine of icmp (mul nsw/nuw X, C2), C

Proof for the future optimisations are here:
- eq/neq: https://rise4fun.com/Alive/9PBA
- sgt/ugt: https://rise4fun.com/Alive/58yr
- slt/ult: https://rise4fun.com/Alive/VCQ

Differential Revision: https://reviews.llvm.org/D51625

llvm-svn: 343190