Fix #2018, false positive -Wstringop-truncation warning

[slyon]

Fix false positive stringop-truncation warning/error with GCC 10 on s390x by indicating GCC to explicitly ignore this case, as it is clearly a false positive (NUL is set in the following line).

This allow the compilation to succeed with -Werror on.

Fixes: #2018

[emersion]

I don't want to clutter the codebase with compiler-specific directives to disable warnings.

[slyon]

Many distributions build with treating warnings as errors, which makes the build fail in this case.
Do you see a better way to improve those two lines of code, to avoid that warning?

[kennylevinsen]

Please see: https://github.com/swaywm/wlroots/wiki/Packaging-recommendations

For upstream, if the code is convoluted, improvement that happens to silence warnings is fine, but we shouldn't bend ourselves out of shape to silence a false positive. It should probably just be disabled in the meson file instead in that case.

[emersion]

Maybe try to pass len - 1, and check if len > 0?

[ascent12]

Many distributions build with treating warnings as errors

Not really related to the issue, but this is a terrible idea for distributors in general. -Werror is a developer thing.
Upgrading your compiler could lead to a massive portion of builds breaking, especially for false-positive heavy warnings like this one.

Instead of carrying workarounds upstream, it's a far better idea to just try and fix whatever is actually causing the warning.

[slyon]

I agree it is better to fix the actual problem, than cluttering the codebase with compiler specific directives.

What about just using strncat instead of strncpy? This will append the trailing \0 automatically, thus no warning.

[emersion]

Thanks!