stage2 x86_64: fix bug in Function.gen
stage2 x86_64: fix bug in Function.gen

Previously, the x86_64 backend would remove code for exitlude relocs
if the jump amount were 0. This causes issues as earlier jumps rely on
the jump being present at the same address.

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