LLR (and also sieve) contains machine code for x86, so you cannot compile this code for ARM devices.
But as you can see here: http://www.primegrid.com/results.php?hostid=936112 a Raspberry Pi3 can do LLR work. You will need an emulator for x86 to do so. It's slow but successful.
This has probably been asked before but are there any plans for a Linux based ARM application that could be used to run PG on a Raspberry PI?