stage2: move x86_64 codegen to arch/x86_64/CodeGen.zig
This mimics steps taken for aarch64 and preps stage2 x86_64
for a rewrite introducing MIR for this arch.
91d93b6395Jakub Konka committed on 10/31/2021, 9:32:39 PM· committed by Andrew Kelleyparentc452d10