At the moment, we only support one compiler per platform. This is the generally same compiler used to build the binaries on julialang.org. We may include more compilers in the future. If you wanted to “Just make it work”, you may be able to get clang using either apk add clang, or by grabbing the x86_64 build of clang from https://github.com/staticfloat/LLVMBuilder/releases (e.g. you can add it as a “source” to your build). You may have to fiddle with the settings though (e.g. isysroot in order to make it find the gcc installation of the standard libraries).