Use the same logic for both deps (including LuaJIT, for which setting
this variable is mandatory) and Nvim: either the eponymous environment
variable if set, or the current software version if not.
Removes annoying warnings when building locally on macOS.
Problem:
Dirs "config", "packaging", and "third-party" are all closely related
but this is not obvious from the layout. This adds friction for new
contributors.
Solution:
- rename config/ to cmake.config/
- rename test/config/ to test/cmakeconfig/ because it is used in Lua
tests: require('test.cmakeconfig.paths').
- rename packaging/ to cmake.packaging/
- rename third-party/ to cmake.deps/ (parallel with .deps/)
