Change the way the jump instructions are outputted in the assembly
output to be PC-relative. This fixes an issue where the addresses in the
output where shifted forward.
The index of an element of a `SortedVector<yield::Tag>` was saved, but
`SortedVector` behaves like a set.
The issue has been fixed by creating a temporary `Tag` instead of trying
to keep a reference to an existing one.
Alessandro Di Federico