[cairo] Enable AM_SILENT_RULES

[Chris Wilson]

Excerpts from Soeren Sandmann's message of Fri Aug 28 12:01:08 +0100 2009:
> One question though: How does it relate to shave? Is it a replacement,
> or are they complementary?

They have different mechanisms for supplying details for
non-standard rules, so it's a replacement for shave. I intend to phase
shave out of the cairo build (or if some else wants to do that for
me... ;-), and afterwards I'll have a clearer understanding of the
difference. I hope given the integration into automake, the silent rules
will develop rapidly.
-ickle