It’s isolated and built per platform. See the packages folder of the repo. LuaJIT is widely accepted as the Lua version to use in games. We use Lua JIT 2.10-beta with support for arm 64.
The openresty version has diverged even more from Lua 5.1 so I don’t really see it as a viable option for Defold.
Fengari is a reimplementation of Lua 5.3 in JavaScript. It’s not really an option and I don’t see how it could work with native extensions for instance.