[cairo] Making configure error message more clear

[Benjamin Otte]

On Thu, 2010-03-25 at 17:04 -0400, Behdad Esfahbod wrote:
> 
> Interesting.  Why pkg-config doesn't do it is not hard to see.  Why shouldn't
> it provide a macro to do that, good q.  I'll fix it in cairo and propose other
> packages doing the same.
> 
I like the idea.
And I remembered that pkg-config is a freedesktop project, so it made a
lot of sense to fix this in pkg-config instead of doing custom hacks in
configure files everywhere.
The result is here:
http://lists.freedesktop.org/archives/pkg-config/2010-March/000502.html

Benjamin