- Move emscripten download into its own script - Refactor the common "CI choice" prompt into its own file. - Move the content of `build/common/ci-common.sh` to the "CI choice" script. - Mention the get-emscripten.sh script in BUILDING.md
- Move emscripten download into its own script - Refactor the common "CI choice" prompt into its own file. - Move the content of `build/common/ci-common.sh` to the "CI choice" script. - Mention the get-emscripten.sh script in BUILDING.md