cmd/compile/internal/ssa: use *obj.LSym in ExternSymbol

Change-Id: I713120f90fd1d2df6698c40622ccac6eae907919
Reviewed-on: https://go-review.googlesource.com/36423
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
diff --git a/src/cmd/compile/internal/ssa/value.go b/src/cmd/compile/internal/ssa/value.go
index b9b35b1..00f2454 100644
--- a/src/cmd/compile/internal/ssa/value.go
+++ b/src/cmd/compile/internal/ssa/value.go
@@ -5,6 +5,7 @@
 package ssa
 
 import (
+	"cmd/internal/obj"
 	"cmd/internal/src"
 	"fmt"
 	"math"
@@ -244,8 +245,8 @@
 // ExternSymbol is an aux value that encodes a variable's
 // constant offset from the static base pointer.
 type ExternSymbol struct {
-	Typ Type         // Go type
-	Sym fmt.Stringer // A *gc.Sym referring to a global variable
+	Typ Type // Go type
+	Sym *obj.LSym
 	// Note: the offset for an external symbol is not
 	// calculated until link time.
 }