New tool: opt-diff.py

This tool allows generating the different between two optimization record
files.  The result is a YAML file too that can be visualized with opt-viewer.

This is very useful to see what optimization were added and removed by a
change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296767 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed