Track undefined sym in the symtab. Remove hack for missing relocs against undef.

src/llvm2ice.cpp

 //===- subzero/src/llvm2ice.cpp - Driver for testing ----------------------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines a driver that uses LLVM capabilities to parse a
@@ skipping 380 matching lines @@
         << "--build-on-read=0 not allowed\n";
     return GetReturnValue(Ice::EC_Args);
   }
 
   Ctx.waitForWorkerThreads();
   Translator->transferErrorCode();
   Translator->emitConstants();
 
   if (UseELFWriter) {
     Ice::TimerMarker T1(Ice::TimerStack::TT_emit, &Ctx);
+    Ctx.getObjectWriter()->setUndefinedSyms(Ctx.getConstantExternSyms());
     Ctx.getObjectWriter()->writeNonUserSections();
   }
   if (SubzeroTimingEnabled)
     Ctx.dumpTimers();
   if (TimeEachFunction) {
     const bool DumpCumulative = false;
     Ctx.dumpTimers(Ice::GlobalContext::TSK_Funcs, DumpCumulative);
   }
   const bool FinalStats = true;
   Ctx.dumpStats("_FINAL_", FinalStats);
   return GetReturnValue(Ctx.getErrorStatus()->value());
 }