They won't crash, because the CPU features are tested before any call to the optimized code is made.
https://github.com/MariaDB/server/blob/10.6/mysys/crc32/crc32c.cc#L542-L564 As the Debian CI undoubtedly runs the basic unit tests that cover crc32 on the minimum hardware, and succeeds, it proves the autodetection is correct.
