As I mentioned before, build-presets.ini is where you look to figure out how to use the build-script. I see several skip-test-lldb and lldb-test-swift-only in there, so it's likely you have to be careful how you run the full lldb testsuite, if it can be run at all.
Find a preset config in there that runs the lldb tests you want and either run that or the flags that it bundles, then you can experiment with changing it if wanted.