bug#81609: 31.0.90; Loading debug overwrites debugger

In debug.el there's a naked setq (with an autoload cookie?)

,----
| ;;;###autoload
| (setq debugger 'debug)
`----

which means that whenever debug is required, the previous value of
`debugger` is silently overwritten. In my case, I set in my config
`debugger` to a custom value and `debug` was being lazy-loaded after it
which was overwriting the value.

I am not sure why this is done, since `debugger` has the value `debug`
by default.

-- Al