[ShrinkWrap] Add optimization remarks to the shrink-wrapping pass

Start by emitting remarks for very basic unsupported cases such as
irreducible CFGs and EHFunclets. The end goal is to be able to cover all
the cases where we give up with an explanation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333972 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed