Standard Lua uses 64-bit integers and double-precision (64-bit) floats.
This flag uses 32-bit integers and/or single floats.
I don't think that a new LuaRT release target with this flag is really needed. This use case is rather rare and LuaRT should already be able to compile with this flag (although I have not tested it yet, some warnings may be thrown).
It may cause problems with some functionnalities (for example using colors in Canvas)