Instead of working at a high level dive down to try and localise the problem. You can use /lib/cpp directly with a simple test case to try and identify the bug.
heh.
/lib/cpp is an actual program and not just a canon of incantations one mumbles while flayling about and scribbling in obscure shell scripts?
Who'd of thunk it?
Thank you.
Doing so would have never occurred to me; it should be fun.
I am going to spend a bit of time refreshing my memory of the buildXYZ.sh scripts and then turn my attention to that.