Thanks to all, using those two libs everything works OK 
i modified the ebuild replacing
Code:
dosym ../xorg-x11/extensions ${ATI_ROOT}/extensions
with this
Code:
exeinto ${ATI_ROOT}/extensions
doexe "${BASE_DIR}"/usr/X11R6/${PKG_LIBDIR}/modules/extensions/libglx.so
doexe "${BASE_DIR}"/usr/X11R6/${PKG_LIBDIR}/modules/extensions/libdri.so
and adding this function to remove the symlink (not sure if this is the correct way to do that)
Code:
pkg_preinst() {
if use amd64 ; then
[[ -L "${ROOT}/usr/lib32/opengl/ati/extensions" ]] && rm ${ROOT}/usr/lib32/opengl/ati/extensions
fi
[[ -L "${ROOT}/usr/lib/opengl/ati/extensions" ]] && rm ${ROOT}/usr/lib/opengl/ati/extensions
}