At present, luasandbox is tied to Lua 5.1, which is so out of date that certain features of Lua 5.2 are backported to luasandbox's implementation of Lua.
Perhaps it is time to move on.
At first, references to Lua version hardcoded into luasandbox source code could be removed and made configurable in the options for `cmake` or `./configure` (defaulting to Lua 5.1).
The hardcoded Lua version is found in `config.cmake` and `config.m4`. The file `FindLua51cpp.cmake` ought to be, I guess, cloned into `FindLua52cpp.cmake` and `FindLua53cpp.cmake` or parametrised somehow.