Link .dynamic to .dynstr

This is what the ELF specification says we should do.
(see Figure 1-13: sh_link and sh_info Interpretation)

Also make the entity size of string sections 0 (i.e. not a table).
Size 1 makes some sense as well but it is not what other tools do.

Bug: 20556771
Change-Id: I780ba2e13c09c33c143fca70b38a35f3b8528fb2