#39 zuidgen test fails to link on mac

[Mat Marcus]

The zuidgen test fails to link on the mac if certain
environment variables are not defined. Build should be
self-contained. One approach would be to add
-libSystemStubs in the pre-10.4 deployment target case.
Also -isysroot seems to be missing from link commands.

[Foster Brereton]

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Fixed in opensource.adobe.com:10666 checkin 366. This will
be reflected in ASL 1.0.18.