Ok, now I see that the 3.6 upstream branch places the samba3-idl target underneath 'make all', so I assume that they are now relying on the code generation to happen at build time. Can you confirm this, Jelmer?
If that's the case, then we probably do want to follow that convention in our 3.6.x and later packages (currently only found in Precise). The reason is that if we don't do it at build time, but upstream does, one of their patches that we cherry-pick could theoritically need to be ran through PIDL to make proper changes. I _think_ that's the case, but I'm still not quite knowldgeable on the PIDL compiler to know for sure.