[Patch, fortran] PR28172, PR29389, PR29712 & PR30283 - some "one liner fixes"

[François-Xavier Coudert]

> What do you want?  A TODO above the check for pureness and a commit that
> permits legal stuff or to leave the tree as it is until I can get to it?
>
> PS The patch is bootstrapping and regtesting right now, so you have ~30
> minutes to tell me what to do :-)

I guess I still have 9 minutes left, and I'm glad I check my email
both during breakfast and as soon as I get back to work! :)

I'd say: leave that part alone, add a comment in the PR saying that
this is only part of the trick. Less work, fewer opportunities to mess
up with the tree, and mixing pure qualifier and statement functions
probably isn't the most used F95 feature.

Thanks,
FX