I don't know the answer to the mix old/new compilers question but it looks like it's only the directory structure of the compiled artefacts that's important rat

I don't know the answer to the mix old/new compilers question but it looks like it's only the directory structure of the compiled artefacts that's important rather than the directory structure of the source code. It looks like you could keep all your source in one directory (unlike Java IIRC) and then compile it with `-I` and `-P` options.