Fix tools/check-parser-uptodate-or-warn.sh

[gasche]

This PR fixes #8965 (a build failure caused by a warning script) by:

• adding support for Busybox' stat to the script
• making the script more robust to unexpected failures
• disabling the script on non-development versions (as suggested by @Octachron)

[dra27]

Rather than peppering the diff with suggestions, I've pushed commits any of which you should feel free to blow away - the only thing which has to be fixed is the overly long line (which I fixed by adding an extra error message)

[gasche]

How portable is this change to different grep implementations? I'm worried about using anything more than the simplest grep command.

[dra27]

I already checked - -F and -q are both POSIX, as is the combination of them to -Fq!

[dra27]

(for the others, the -F is overkill, for this one it seems sensible in case some naughty grep treats + as magic without enabling EREs)

[XVilka]

By the way, I recommend to use shellcheck tool (and it integrates nicely with both Vim and Emacs) for checking the shell scripts on portability issues and such, they even have an online interface.

[XVilka]

May I ask, when this landed in the trunk, will it be a part of the future 4.09.1 release, or only for 4.10.0 one?

[dra27]

There's no reason not to push it to the 4.09 branch, but there's no guarantee that there will be a 4.09.1 release.

[gasche]

(I decided to wait for the INRIA CI reports before backporting into 4.09.)