Execution ABI and targets

Every dk build runs under an execution ABI that names the host it runs on, and resolves objects for a target ABI. Because dkjs always runs on Node.js, its execution ABI is always js_nodejs, with an operating-system value of JS and an OS family of js. dkjs does not probe the machine underneath Node: it never resolves native per-ABI artifacts, so the host CPU and operating system do not change how it runs.

A build targets js_nodejs by default, or js_web (set with --target-abi) to produce web-bundler output. Native target ABIs are not available yet (see Scope).