Run cachegrind output through rustfilt

[erikdesjardins]

I have valgrind-3.16.1, which should be able to demangle Rust symbols (according to the changelog, support was added in 3.13.0), but it doesn't do a very good job...

e.g. cargo +nightly run --release --bin collector -- diff_local cachegrind --include helloworld --builds Opt --runs IncrUnchanged +3b3ce374d203445eb1d0dce50f4211f4aceb7db6 +20997f6ad81721542e9ef97bb2f58190903a34d8 outputs:

-10,848  ???:rustc_query_system::query::plumbing::incremental_verify_ich
 -6,532  ./string/../sysdeps/x86_64/strcmp.S:strcmp
  5,320  ???:_ZN18rustc_query_system5query8plumbing22incremental_verify_ich17h7b6e470314c3c592E
 -3,960  ???:llvm::PMDataManager::initializeAnalysisImpl(llvm::Pass*)
  3,945  ???:llvm::PassRegistry::registerPass(llvm::PassInfo const&, bool)
  2,792  ???:_ZN18rustc_query_system5query8plumbing22incremental_verify_ich17hd69396997e117d33E
  2,736  ???:_ZN18rustc_query_system5query8plumbing22incremental_verify_ich17h6c9f4a8f7833e3a5E
...

(with rustfilt the incremental_verify_ich clones get demangled and they cancel out)

[Mark-Simulacrum]

Yeah, I've seen the same as well. Not sure what is up with cachegrind, but seems reasonable to just patch over it.