Rebootstrapping ARM64 is needed. We have newer gcc, and zstandard seems to have matured. I got stuck on gcc atomic handling when I tried a few weeks with gcc11, but it might work better with gcc13.
gcc has a way (libatomic) to detect and use correct functions depending on ARM64 atomic support. I think we should just focus on boards that supports the LSE extension instead of dynamic runtime detection and additional function call, but perhaps someone has arguments against that…