[release-branch.go1.11] cmd/link: revise previous __DWARF segment protection fix

Tweak the previous fix for issue 32673 (in CL 182958) to work around
problems with c-shared build mode that crop up on some of the builders
(10.11, 10.12).  We now consistently set vmaddr and vmsize to zero
for the DWARF segment regardless of build mode.

Fixes #32696.

Change-Id: Id1fc213590ad00c28352925e2d754d760e022b5e
Reviewed-on: https://go-review.googlesource.com/c/go/+/183237


Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/183400
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>