[link error] Binding to external libraries

Hello there,
the docu suggests appending the lib and the libpath to the module related env object. But it seems, that this is not the way how it works. I had to append everything to the godot global env object.
[click here](https://docs.godotengine.org/en/3.1/development/cpp/binding_to_external_libraries.html)

> To add include directories for the compiler to look at you can append it to the environment’s paths:
>
> ```
> env_tts.Append(CPPPATH=["speech_tools/include", "festival/src/include"]) # this is a path relative to /modules/tts/
> # http://www.cstr.ed.ac.uk/projects/festival/manual/festival_28.html#SEC132 <-- Festival library documentation
> env_tts.Append(LIBPATH=['libpath']) # this is a path relative to /modules/tts/ where your .a library files reside
> # You should check with the documentation of the external library to see which library files should be included/linked
> env_tts.Append(LIBS=['Festival', 'estools', 'estbase', 'eststring'])
> ```

The necessary suffix for the libs should also be mentioned; For more details check this: [click me](https://github.com/godotengine/godot/issues/23687)