In xgl-0.0.1_pre20060823.ebuild PATCHES is defined incorrectly as ${FILESDIR}/xgl-mesa-slang_pp_version.diff but in the tar ball the diff-file is actually xgl-mesa-symlink-slang_pp_version.diff. Change PATCHES to: PATCHES="${FILESDIR}/xgl-mesa-symlink-slang_pp_version.diff ${FILESDIR}/xgl-xinerama-20060823.patch" resolves the problem.
Which overlay is this from? It's not in the main tree.
Not in portage.
It's in portage-xgl. This seems to be a problem with xgl-coffee.org's overlay. I apologize for incorrectly filing this.