The benchmarks themselves aren't really specific to `driver`.
Keeping the source generation near to the primary use case of
benchmarking also seems like a more discoverable location.
I feel a little bad doing this reorganization right after I gave a talk
with links to a bunch of this code, but seems good to reorganize a bit
before doing some work to extend things now that we have full standard
library support for C++ benchmarking and other improvements.
Assisted-by: Antigravity with Gemini
Chandler Carruth
e041afd98d