Any way to allow tunables to include small headers?

[Florian Weimer]

* Carlos O'Donell:

> I was thinking a micro-header that defines just the defaults, and we
> use it in C code and the tunables list file. That would mean allowing
> a include to pass through scripts/gen-tunables.awk and that could set
> dangerous precedent :-)

It might be nicer to extract the defaults from the tunables list file
and generate a C header from that.  This avoids the need for include
file processing for tunabe list files (for now).