The ebuild for x11-libs/cairo-1.7.4 has >=x11-libs/pixman-0.10.0 as dependency, but it needs >=x11-libs/pixman-0.11.2 (see build.log).
Created attachment 166461 [details] build.log
+ 26 Sep 2008; Peter Alfredsen <loki_val@gentoo.org> cairo-1.7.4.ebuild: + Fix bug #238722, depend on pixman ge 0.11.2 +