I'm pretty sure you're not supposed to install config.h. The reason is
that all autoconfiscated packages have a config.h, and they all define
the same symbols but with different values, so there's a high chance of
symbol clashes. Right now I'm unable to use my own config.h without the compiler complaining.
If you want to make available, for instance, Octave's VERSION string, you're supposed to have a .h that says
When the cc is compiled, it gets the VERSION string from the config.h,
but when octave is installed, you don't need to install config.h to
have the version information for octave. (Mutatis mutandis for directories etc...)