[Xcb] demo/util fixes for the extension split

[Donnie Berkholz]

Vincent Torri wrote:
> Hey !
> 
> I don't think it's the correct patch, for 2 reasons :
>  * the name of the splitted library can change later (it would be strange,
> yes)
>  * more important, the location of the splitted extension can be else
> where that xcb-aux one.
> 
> I've added in bugzilla a fix, which adds a .pc for each splitted
> extension. It works (Ive also made the changes for xcb-utils and
> xcb-demo, and another lib that uses xcb). I wait for an answer from the
> devs.

That might be a more useful way to go. I didn't feel like doing that 
much work and instead made something that should work in most cases.

Donnie