debug/dwarf: read DWARF 5 cu base offsets on SeekPC() path
This patch fixes a bug in CL 655976 relating to DWARF 5 support; we
were reading in compile unit base offsets on the Seek() path but not
on the corresponding SeekPC path (we need the offsets to be read in
both cases).
Updates #26379.
Fixes #72778.
Change-Id: I02850b786a53142307219292f2c5099eb0271559
Reviewed-on: https://go-review.googlesource.com/c/go/+/656675 Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>