Migrate WholeProgramDevirt to new Optimization Remark API

Summary:
This is an attempt to move WholeProgramDevirt to the new remark API.

https://bugs.llvm.org/show_bug.cgi?id=33793

Reviewers: anemet

Reviewed By: anemet

Subscribers: fhahn, llvm-commits

Differential Revision: https://reviews.llvm.org/D36943

llvm-svn: 311352