When --enable-x11 is passed to ./configure for media-sound/pulseaudio-0.9.15, it checks for the existance of four libraries via pkg-config: x11 ice sm xtst. The DEPEND/RDEPEND for the pulseaudio ebuild, however, only requires three of them: libX11, libICE, and libSM. There is a hard failure if libXtst is not also installed.
+ 09 May 2009; Samuli Suominen <ssuominen@gentoo.org> + pulseaudio-0.9.15.ebuild: + Missing x11-libs/libXtst dep for USE X wrt #267286