6g misparses negative constants in imports

R=r
DELTA=8  (8 added, 0 deleted, 0 changed)
OCL=15893
CL=15898

test/bugs/bug106.dir/bug0.go

+// Copyright 2009 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 bug0
+export const A = -1

test/bugs/bug106.dir/bug1.go

+// Copyright 2009 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 bug1
+import "bug0"
+

test/bugs/bug106.go

+// $G $D/$F.dir/bug0.go && $G $D/$F.dir/bug1.go || echo BUG: failed to compile
+
+// Copyright 2009 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.
+
+ignored