NewGVN: Handle coercion of constant stores, loads, memory insts.

Summary:
Depends on D30928.

This adds support for coercion of stores and memory instructions that do not require insertion to process.
Another few tests down.
I added the relevant tests from rle.ll

Reviewers: davide

Subscribers: llvm-commits, Prazek

Differential Revision: https://reviews.llvm.org/D30929

llvm-svn: 299330