bug#22306: 24.5; Unhide --no-line-directive Documentation

[Eli Zaretskii <eliz@gnu.org>]

> From: James Muchow <jim_muchow@dell.com>
> Date: Mon, 4 Jan 2016 19:41:28 +0000
> 
> In trying to create a TAGS file, etags would process the
> #line directive in various source files and produce TAGS 
> files that were unusable because the "file name" included
> would be unavailable causing the tags-search to exit before
> having seen all files.
> 
> I spent a lot of time coming up with a solution to avoid
> any files that contained a line directive when the solution
> I really needed was already present: --no-line-directive.
> It is, however, undocumented and thus the only way to know
> about it is to download the source. I downloaded the source
> to try and find out what etags was doing wrong with #line
> when I discovered this undocumented option.
> 
> I see from the source that the --no-line-directive is hidden
> by the PRINT_UNDOCUMENTED_OPTIONS_HELP; I think it would be
> helpful for others to remove this restriction.

Francesco,

Are there any reasons to keep this option (and a few others) hidden
from the user eyes?

Thanks.