luaK_setreturns
#define luaK_setmultret(fs,e) luaK_setreturns(fs, e, LUA_MULTRET)
LUAI_FUNC void luaK_setreturns (FuncState *fs, expdesc *e, int nresults);
luaK_setreturns(fs, e, extra); /* last exp. provides the difference */