base: Handle backfilling in anonymous python code, not event handler
Handling of backfilling is trickier than you'd think. We need this to execute
early enough that the user will see the changes in bitbake -e and other output
yet late enough that the virtclass extensions have changed the tunes before
it executes.
It makes more sense to execute this at anonymous python time now bitbake -e
correctly handles this and that unbreaks multilib corruption of these variables.
[YOCTO #12373]
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
