[LVI][CVP] Constrain values in with.overflow branches

If a branch is conditional on extractvalue(op.with.overflow(%x, C), 1)
then we can constrain the value of %x inside the branch based on
makeGuaranteedNoWrapRegion(). We do this by extending the edge-value
handling in LVI. This allows CVP to then fold comparisons against %x,
as illustrated in the tests.

Differential Revision: https://reviews.llvm.org/D60650

llvm-svn: 358597