How to do a profiling build?

I'm not very familiar with Nix, and thus am not sure what I'd need to do to allow me to profile the code in here. This is related to work stemming from [this PR](https://github.com/input-output-hk/cardano-base/pull/253#issue-1109867304), and ultimately seeking to address one of the issues described [here](https://github.com/input-output-hk/cardano-base/pull/252#issuecomment-1016706315).