Yeah, that's not good that yet another version of clang is popping in there. 
More importantly, most people use one of the build presets to get all the relevant tools and libraries installed in a toolchain directory, rather than trying to construct a build-script invocation with a bunch of flags themselves. Take a look at utils/build-presets.ini for some common presets that you can try, and what flags they bundle together, if you still want to try writing your own.