Error when building luarpc

When trying to build luarpc, the build errors.
```
src/modules/bit.c:43:8: error: ‘s64’ undeclared (first use in this function)
   43 |   ( ( (s64)luaL_checknumber((L), (n))) & 0x0ffffffff  )
```
I tried to declare it like this in bit.c
```
/* Quickfix */
typedef signed long long s64;
```

This builds the projet, but I'm unsure if it is the proper solution?