Mark usage function as __dead2 in programs where it does not return

[AtariDreams]

In most cases, usage does not return, so mark them as __dead2. For the cases where they do return, they have not been marked __dead2. Yes, all cases were checked.

[delphij]

Looks good to me.

[ngie-eign]

Please change the email address to a non-users.noreply.github.com based address.
If you use git config user.email, etc, then run git commit --reset-author --amend, it will update the authorship appropriately.

[bsdimp]

So what does this offer over and above the _Noreturn marker for exit()? In the past we've not added this to the entire call tree that doesn't return, just the leaves, which the compiler can then infer is no-return... Help me understand what benefit there is here.

[AtariDreams]

So what does this offer over and above the _Noreturn marker for exit()? In the past we've not added this to the entire call tree that doesn't return, just the leaves, which the compiler can then infer is no-return... Help me understand what benefit there is here.

For consistency with the other functions already marked as dead2

[bsdimp]

OK. That makes sense. Most of the current ones don't really need that since the compiler can guess.
Consistency is good. _Noreturn is the new standard for this stuff, but it's likely not worth it to do that here.

[bsdimp]

landed. But for next time:
Break changes up into smaller chunks. I broke this into 15 changes with 10-25 files each.
Also had to fix the commit message to be < 80 characters.