cmd/internal/obj: move dwarf.Var generation into compiler

Passes toolstash -cmp.

Change-Id: I4bd60f7ebba5457e7b3ece688fee2351bfeeb59a
Reviewed-on: https://go-review.googlesource.com/37874
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alessandro Arzilli <alessandro.arzilli@gmail.com>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/internal/obj/link.go

@@ -32,6 +32,7 @@ package obj
 
 import (
 	"bufio"
+	"cmd/internal/dwarf"
 	"cmd/internal/src"
 	"cmd/internal/sys"
 	"fmt"
@@ -752,6 +753,7 @@ type Link struct {
 	Armsize       int32
 	Pc            int64
 	DiagFunc      func(string, ...interface{})
+	DebugInfo     func(fn *LSym) []*dwarf.Var
 	Mode          int
 	Cursym        *LSym
 	Version       int