Just added `--cfg-print` that should do what you were looking for, to the extent of evaluating `include_file/import_file` and `ifdef/ifndef` conditions.
It does not replace the tokens defined with `define`, `subst` or the other token defining variants. If someone needs to go further into this, then a pull request is more than welcome.
Basic tests were done with default config file and an imported file. If there are issues, open a bug report.
As a side note, to be aware of, the empty lines are kept, so the output may have sequences of several empty lines, if the `#!ifdef ... #!endif` blocks had empty lines before and after.