[BOLTDIFF] Add a tool to audit performance differences

Summary:
This is a simple bolt-based tool that instantiates two
RewriteInstances objects and compares them. Add a method to
RewriteInstance to enable us to compare two objects. Include a mechanism
to match functions from binary 1 to binary 2 and finally print the
largest differences in profiling data from one binary to another.

(cherry picked from FBD6517076)