link error
I'm having a hard time linking liblua.a during the build process.

```
$ make
...
g++ bin/main.o bin/hal_core.o bin/hal_palette.o bin/hal_audio.o bin/pico_core.o bin/pico_audio.o bin/pico_memory.o bin/pico_data.o bin/pico_script.o bin/pico_cart.o bin/utf8-util.o bin/utils.o bin/log.o bin/crypt.o -L/usr/lib -lSDL2 -Lsrc/z8lua -llua -o tac08
/usr/bin/ld: bin/pico_script.o: in function `dbg_hookfunc(lua_State*, lua_Debug*)':
pico_script.cpp:(.text+0xa7): undefined reference to `lua_getstack(lua_State*, int, lua_Debug*)'
...
# 100 or so additional undefined reference errors from pico_script.cpp
```

But I can see that those symbols exist in liblua.a

```
$ nm -g src/z8lua/liblua.a | c++filt | grep lua_getstack
0000000000000540 T lua_getstack(lua_State*, int, lua_Debug*)
                 U lua_getstack(lua_State*, int, lua_Debug*)
                 U lua_getstack(lua_State*, int, lua_Debug*)
                 U lua_getstack(lua_State*, int, lua_Debug*)
```

The linker flags are the makefile default

```
LUA_LIB =  -Lsrc/z8lua -llua
LDFLAGS = $(SDL_LIB) $(LUA_LIB)
```

I'm on x86-64 Linux, GCC 9.1.0, binutils 2.32.
