Atomic ARC

[guzba]

AMD Ryzen 5 5600x + Windows 10 for this benchmark

`mm: arc; threads: on; opt: speed; options: -d:release 165616 lines; 8.583s; 
489.793MiB peakmem`

`mm: atomicArc; threads: on; opt: speed; options: -d:release 165616 lines; 
8.646s; 489.805MiB peakmem`