Check struct sizes on the CI instead of during compile-time

[DL6ER]

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Check struct sizes on the CI (in code) instead of during compile-time (using the preprocessor). This should resolve an issue reported on Discourse.

It adds an (undocumented) new flag pihole-FTL --check-structs that is supposed to be used by the tests. The exit code will tell if everything worked as expected (bash-compatible: exit code 0 is success).

[dschaper]

Thanks!

[DL6ER]

It's worth pointing out that we will only test struct sizes on platform where we run the tests for (x86, x86-musl, i386). However, this is not a drawback as we are checking on both 32bit and a 64bit architectures. (also note that there is no difference between arm, mips and i386 so everything is still covered).

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pi-hole-ftl-v5-16-web-v5-13-and-core-v5-11-1-released/56384/1