Following Godot Example on macos breaks

Running `scons target=debug` [as described](https://godotengine.org/article/introducing-gd-extensions/#building-the-test-plugin) breaks on macos.
```
scons: Reading SConscript files ...

Auto-detected 16 CPU cores available for build parallelism. Using 15 cores by default. You can override it with the -j argument.

scons: *** Invalid value for option target: debug. Valid values are: ('editor', 'template_release', 'template_debug')
File "/godot-cpp/SConstruct", line 157, in
```

Documentation on the page probably should be updated to reflect that it's `scons target=editor` or `scons target=template_debug`.

Finally running `scons target=editor` produces:
```
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
scons: *** [src/core/class_db.macos.editor.universal.o] Error 1
scons: building terminated because of errors.
```

You need to actually specify `scons target=editor arch=x86_64` for a successful build.