Fix .rel.plt sections in the output to not only include .rel.plt
sections from the input but also the .rel.iplt sections and to define
the hidden symbols __rel_iplt_start and __rel_iplt_end around
.rel.iplt as otherwise we get undefined references to these when
linking statically to a multilib libc.a. This fixes the static build
Apply similar logic to rela.plt/.iplt and __rela_iplt/_plt_start/_end to
fix the static build under amd64.