Propagate nonnull and dereferenceable throught launder

Summary:
invariant.group.launder should not stop propagation
of nonnull and dereferenceable, because e.g. we would not be
able to hoist loads speculatively.

Reviewers: rsmith, amharc, kuhar, xbolva00, hfinkel

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D46972

llvm-svn: 332788