Use a package searcher to static link LuaSocket into an executable.

modules.c

#include <stddef.h>
#include <string.h>

#include <lua.h>
#include <lauxlib.h>

#include "luasocket/src/ftp.lua.h"
#include "luasocket/src/headers.lua.h"
#include "luasocket/src/http.lua.h"
#include "luasocket/src/ltn12.lua.h"
#include "luasocket/src/mbox.lua.h"
#include "luasocket/src/mime.lua.h"
#include "luasocket/src/smtp.lua.h"
#include "luasocket/src/socket.lua.h"
#include "luasocket/src/tp.lua.h"
#include "luasocket/src/url.lua.h"

int luaopen_mime_core(lua_State*);
int luaopen_socket_core(lua_State*);

typedef struct
{
    const char* name;

    union
    {
        const char* source;
        lua_CFunction openf;
    };

    size_t length;
}
module_t;

#define MODL(name, array) {name, {array}, sizeof(array)}
#define MODC(name, openf) {name, {(char*)openf}, 0}

static const module_t modules[] =
{
    MODL("ltn12", socket_ltn12_lua),
    MODL("mbox", socket_mbox_lua),
    MODL("mime", socket_mime_lua),
    MODC("mime.core", luaopen_mime_core),
    MODL("socket", socket_socket_lua),
    MODC("socket.core", luaopen_socket_core),
    MODL("socket.ftp", socket_ftp_lua),
    MODL("socket.headers", socket_headers_lua),
    MODL("socket.http", socket_http_lua),
    MODL("socket.smtp", socket_smtp_lua),
    MODL("socket.tp", socket_tp_lua),
    MODL("socket.url", socket_url_lua)
};

#undef MODL
#undef MODC

static int searcher(lua_State* const L)
{
    const char* const name = lua_tostring(L, 1);

    for (size_t i = 0; i < sizeof(modules) / sizeof(modules[0]); i++)
    {
        if (strcmp(name, modules[i].name) == 0)
        {
            if (modules[i].length != 0)
            {
                const int res = luaL_loadbufferx(L, modules[i].source, modules[i].length, name, "t");

                if (res != LUA_OK)
                {
                    return lua_error(L);
                }
            }
            else
            {
                lua_pushcfunction(L, modules[i].openf);
            }

            return 1;
        }
    }

    lua_pushfstring(L, "unknown module \"%s\"", name);
    return 1;
}

void registermods(lua_State* const L)
{
    lua_getglobal(L, "package");
    lua_getfield(L, -1, "searchers");
    const size_t length = lua_rawlen(L, -1);

    lua_pushcfunction(L, searcher);
    lua_rawseti(L, -2, length + 1);

    lua_pop(L, 2);
}