Does 10.6 have an SDK in /Developer/SDKs/ ? If so, you need to edit makepandacore.py and makepanda.py and replace “10.5” by “10.6”.
“rm -rf built” before you try again building.
Also, you can try finding the line in makepanda.py that contains “-lOSMesa” and try uncommenting it. I don’t know why it’s needed.