If the Sphinx was built before they had mapped constellations, the orientation sync'ed with Leo would seem too much of a coincidence, unless maybe it happened the other way around: and the constellation was named according to the monument.
(Btw, the 6000 BCE came from this site) http://en.wikipedia.org/wiki/Zoroaster
From an archaeological perspective, Gobekli Tepe is still a "new" site and, over the forthcoming years of research and evaluation, there will be quite an amount of effort invested into the interpretations of this site. Nonetheless, some credible radiocarbon dates have been produced. In the following you will note the extensive detail being incorporated into attempting to refine occupational sequences/activities:
You may also find the corroborating lithic analysis to be of interest: