staticdata: encode link_id in tagged linkage (#48673)
On 64-bit, we have enough space to encode (1) the tag, (2) the
`depmods` index, and (3) the offset all in a single 64-bit pointer
field. This means we don't need the external `link_id` arrays,
which reduces the size of many pkgimages by ~5%.
On 32-bit, we don't have enough bits to implement this strategy.
However, most linkages seem to be against the sysimage, and so
by giving that a separate tag we can achieve similar compression
because the `link_id` lists will be much shorter.
Co-authored-by: Tim Holy <tim.holy@gmail.com>
