Ahh good question. I had to think a while before I understood what you meant. Let me check when I can.
Nice catch.
edit: you are right. The binary version will result in a different argv[0]. Not sure what'd the best solution would be. Hardcoding doesn't make sense, as symlinks also change argv[0], so overriding is not the way to go.
Swift Caching Compiler - https://github.com/jrz/tools