Author here. The makefiles I'm using are on github:

https://github.com/dwrensha/capnproto-rust/blob/master/Makef...

https://github.com/dwrensha/capnproto/blob/benchmark/c%2B%2B...

I compiled libcapnp with the latest Clang g++ that ships with XCode. It perhaps would be more fair to also compile the C++ benchmarks with Clang, instead of the Macports gcc4.8 that I'm using, but unfortunately Clang barfs on some template hackery in the benchmark driver.