Finally found the reason the MariaDB 11.8 releases do not run on this quite old AMD server: the AM2/AM2+ architecture is too old. (It's missing the PCLMULQDQ instruction flag.)

I went through the trouble of setting up a test server on a MiniPC (Intel NUC NUC6AYH), and it does run there. Though, I forgot to run lscpu for the instruction flags... so I searched for it online, and that NUC's CPU does indeed have the flag.

I then actually compiled the source on an even older Dell Latitude D830 and executed it. Same illegal instruction (SIGILL) as on the aging server. It does not have the flag.

It does run on my main laptop that has a high-end Sandy Bridge CPU, which has the flag.

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From the AMD server and main laptop logs:

MariaDB 11.4: InnoDB: Using generic crc32 instructions
MariaDB 11.8: InnoDB: Using crc32 + pclmulqdq instructions