sys/auto_init: initialize app code from auto_init [RFC]

[vincent-d]

Contribution description

A new weak function auto_init_app is called at the end of the auto_init
function to let the app initializing its own modules before main is
called.

This is a RFC. My main goal is to make the initialization of our different app and modules more generic and transparent.
So far we call our own 'auto_init' from the beginning of main, but it would be more transparent to use this hook.

Issues/PRs references

None

[kaspar030]

My main goal is to make the initialization of our different app and modules more generic and transparent.

I must say I don't see the benefits outweigh the problems this might cause:

• we'll have users not using this but use their own explicitly called init function. Do we make them use auto_init_app for consistency?
• we might soon introduce "multi-app" builds. Those would need to be changed, as this concept only allows one auto_init_app
• without linking fixes, this breaks if auto_init_app is the only used symbol of the compilation unit it is defined (see make: fix linking #5757). So there will either be frustrated or help-searching users. ;)

#7523 will allow AUTO_INIT(myfunc, priority); in any compilation unit, would that serve your needs?

[vincent-d]

I guess #7523 is a better solution, indeed. Let's close this.