lto/addAsmGlobalSymbols: fail fracefully when the target does not define AsmParser.

lib/Target/PNaCl/PNaCl.h

+//===-- PNaCl.h - Top-level interface for PNaCl representation --*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains the entry points for global functions defined in the LLVM
+// PNaCl back-end.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef TARGET_PNaCl_H
+#define TARGET_PNaCl_H
+
+#include "MCTargetDesc/PNaClMCTargetDesc.h"
+#include "MCTargetDesc/PNaClMCAsmInfo.h"
+#include "llvm/Target/TargetMachine.h"
+
+namespace llvm {
+  class PNaClTargetMachine;
+  class FunctionPass;
+  class formatted_raw_ostream;
+} // end namespace llvm;
+
+#endif