Profile incremental compilation hashing fingerprints
Adds profiling instrumentation for the hashing of incremental compilation fingerprints per query.
This will eventually feed into the `measureme` and `rustc-perf` infrastructure for tracking if computing hashes changes over time.
TODOs:
* [x] Address the FIXME where we are including node interning in the hash timing.
* [ ] Update measureme/summarize to handle this new data: https://github.com/rust-lang/measureme/pull/166
* [ ] ~Update rustc-perf to handle the new data from measureme~ (will be done at a later time)
r? `@ghost`
cc `@michaelwoerister`
bors
f913a4fe90