stage2 aarch64: assert register is 64bits in PCrel
stage2 aarch64: assert register is 64bits in PCrel

Thanks @joachimschmidt557 for pointing out this fix!

andrewrk/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,zig-lang/zig,raulgrell/zig,andrewrk/zig,zig-lang/zig,raulgrell/zig,zig-lang/zig