Support `--debug` mode on Linux

The `--debug` option from #2147 has now been implemented on every platform except Linux.

@timrid: can you add some notes here about why it isn't supported on Linux, and any ideas you've had for how to do it?

Start by reading issue #2147 and tracing the existing `--debug` implementations for the supported platforms. Then determine where Linux handling belongs and document why it is currently unsupported, along with a feasible implementation direction. Done means Linux supports `--debug` consistently with the other platforms and the rationale is recorded.

Written by the indexing model from the issue text.