[RFA] libiberty warning fixes for OSX

[Andrew Cagney]

> Should the declaration be deleted?  I believe that everything now uses 
>> lbasename() (well at least it did a few months ago).
> 
> 
> I hesitate to do so, as it would create a backwards compatibility
> issue.  Even if nothing *we* know of should use it (in which case, the
> declaration is harmless), there may be other packages that we don't
> know about that require it.

Hmm, forgot that there was also a corresponding libiberty/basename.c.

How about remove the header declaration, but leave the corresponding 
(optional) function?

> Perhaps, though, we need better protection for it.  I wish there were
> a way for libiberty's configure to configure the include directory
> headers also.  Sigh.

That way the functionality remains but libiberty.h doesn't publish it. 
Hint to liberty users that its going away :-)

Andrew