Updating older code from OS X 10.6 to 10.7

I'm trying to update ODBCQueryTool so it builds under 10.7. It was originally targeted against 10.6, which is not directly supported in newer versions of Xcode. For now a working build would be fine, but ideally I'd like to make a version that builds and runs on 10.5 or newer. So to start I downloaded and installed the 10.6 SDK. A number of problems disappeared at that point, but I got a series of these: ld: warning: `directory not found for option` `'-F/Users/maury/Develop/odbckit/ODBCQueryTool/../ODBCKit/build/Release`' ``` Undefined symbols for architecture x86_64: "_OBJC_CLASS_$_NSMutableOrderedSet", referenced from: objc-class-ref in libarclite_macosx.a(arclite.o) ``` I can't find anything useful in Google. I was under the impression that ARC was part of 10.7 and newer, so it's not clear why I get these at all.