[cairo] Another set of OSX Build Instructions

[mpsuzuki at hiroshima-u.ac.jp]

>> And, giving the list of backends detected/enabled by
>> default would be helpful.
> 
> Noted at the top, as well in an explanation farther down about why -- 
> disable-xlib is turned on.

I'm sorry, I didn't clarify what I wished...
I wish if you could copy the end of the output
by ./configure, something like:

The following surface backends:
...
   Quartz: ...
   Quartz-image: ...
...

It is helpful for users to check their configuration
was correctly finished, or there is anything wrong.

Regards,
mpsuzuki