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

lib/Target/PNaCl/MCTargetDesc/PNaClMCAsmInfo.h

+//=====-- PNaClMCAsmInfo.h - PNaCl asm properties -------------*- 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 declaration of the PNaClMCAsmInfo class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef PNACLTARGETASMINFO_H
+#define PNACLTARGETASMINFO_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/MC/MCAsmInfo.h"
+
+namespace llvm {
+  class Target;
+
+  struct PNaClMCAsmInfo : public MCAsmInfo {
+    explicit PNaClMCAsmInfo(const Target &T, StringRef TT);
+  };
+
+} // namespace llvm
+
+#endif