config and opt_*h files, how it works?

[TSaplin Mikhail]

I want add some my own options to kernel.
I've add "U04_KOI8R opt_cdunicode.h" to sys/conf/options,
and #include "opt_cdunicode.h" to source files.

But when i do make depend, mkdep cant find opt_cdunicode.h
Whats wrong and how it works?