According to config(9), defflag without a filename causes a command-line
macro to be defined.  For example, cc ... -DFOO.  But, what really happens
is a command-line macro is defined _and_ an option file is created (based
on the lowercase of the option name), such as opt_foo.h.

config could be changed to match the manpage, but will result in a bit of
fall-out since there are several options (for various archs) defined with
defflag that lack a filename.  I did not check if those files are actually
used in any of these cases (except sparc:BLINK, where the file is used)
and defparam (and the deprecated defopt) likely act similarly.

Defining an option in a kernel config that is not defined with defflag,
does result in a command-line macro, but then config does not perform
syntax checking.

So, assuming the extra opt_*.h file is no big deal (I don't think it is),
just fixing the man page for config(9) seems appropriate.  Perhaps I'm
missing some history, such as a transition plan to make the filename
required.  Opinions?

-heas