OpenAl build only works with makepanda, however makepanda is not running under osx. ppremake has no openal support (at least 1.4.x had it not included).
So you eighter need to apply the patches available for ppremake-openal (look in the mac build thread). Or you try to continue the work on makepanda, which is not yet completed afaik.
The other possibility, which i recommend, is to use fmod(ex).
Until these issues are fixed by someone (or somebody is willing to include/check the patches i provided).