Add fallbacks for ARMv8a to make it compile

The current code, on ARM, uses ARMv8.1-A RDM instructions. Add a fallback for processors that do not have this instruction set.

Add some specific compile options for this platform.

Add debian 12 to the list of architectures.

Currently, we don't have a platform to run this, nevertheless i put BUILD-ONLY to verify that the build on the remaining architectures is fine.