An Even-More-Basic Earthly Project (#1395)

* An earthly.sh shim script
* Tweak find-cmake to use download.sh for downloader-agnosticism.
* A cmake.sh shim to run the managed CMake version
* Fix checks in ResSearch, since libmusl does not have res_close
* Add a simple Earthfile with a few platforms
* Add EVG Earthly tasks