[release-branch.go1.12] 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 #32697
    
    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/+/183398
    Run-TryBot: Cherry Zhang <cherryyz@google.com>
    TryBot-Result: Gobot Gobot <gobot@golang.org>