cmd/5l, cmd/6l, cmd/8l: fix segfault on reading LOCALS for a duplicate definition.

Fixes #5105.

R=golang-dev, dave, daniel.morsing, rsc
CC=golang-dev
https://golang.org/cl/7965043

src/cmd/5l/obj.c

@@ -608,11 +608,15 @@ loop:
 		break;
 
 	case ALOCALS:
+		if(skip)
+			goto casedef;
 		cursym->locals = p->to.offset;
 		pc++;
 		break;
 
 	case ATYPE:
+		if(skip)
+			goto casedef;
 		pc++;
 		goto loop;
 

src/cmd/6l/obj.c

@@ -597,11 +597,15 @@ loop:
 		goto loop;
 
 	case ALOCALS:
+		if(skip)
+			goto casdef;
 		cursym->locals = p->to.offset;
 		pc++;
 		goto loop;
 	
 	case ATYPE:
+		if(skip)
+			goto casdef;
 		pc++;
 		goto loop;
 

src/cmd/8l/obj.c

@@ -607,11 +607,15 @@ loop:
 		goto loop;
 
 	case ALOCALS:
+		if(skip)
+			goto casdef;
 		cursym->locals = p->to.offset;
 		pc++;
 		goto loop;
 
 	case ATYPE:
+		if(skip)
+			goto casdef;
 		pc++;
 		goto loop;
 

test/fixedbugs/issue5105.dir/a.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package a
+
+var A = [2]string{"hello", "world"}

test/fixedbugs/issue5105.dir/b.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "./a"
+
+var B = [2]string{"world", "hello"}
+
+func main() {
+	if a.A[0] != B[1] {
+		panic("bad hello")
+	}
+}

test/fixedbugs/issue5105.go

+// rundir
+
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 5105: linker segfaults on duplicate definition
+// of a type..hash.* function.
+
+package ignored