Fix strlen buffer overrun

[a1akris]

Basically the syntax to declare a flexible array member like this char* regd_name[0] has become so obsolete that it's treated as a zero sized string regardless of its contents, therefore __fortify_stlren was crashing while trying to read the first byte.

This also reverts #332 as it's not needed anymore.

[Desour]

Tested. Works, this fixes the crash at shutdown with the blinking caps lock.

The linux kernel uses gnu C11 since 5.18 (see https://www.kernel.org/doc/html/v5.18/process/programming-language.html) (gnu C90 before).
ISO C99 flexible array members should be available at least since then. So you could lower the kernel version in the #ifs.

[Spixmaster]

@tomaspinho Since we have two external tests by @Desour and @dexter2000 which prove the functionality, could you merge this pull request?

[leandrocunha526]

Issue #335 it was resolved with this.

[tomaspinho]

Thanks for fixing the root cause!