cmd/internal/objfile: use aux symbol for pcdata references

cmd/internal/objfile: use aux symbol for pcdata references

Pcdata are now separate aux symbols. Read them from aux, instead
of using funcinfo.

Change-Id: Ib3e4b5cff1e3329d0600504a8829a969a9c9f517
Reviewed-on: https://go-review.googlesource.com/c/go/+/352612
Trust: Cherry Mui <cherryyz@google.com>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>