Subzero: Add -allow-extern as an alias for --allow-externally-defined-symbols.

src/IceConverter.cpp

 //===- subzero/src/IceConverter.cpp - Converts LLVM to Ice  ---------------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 854 matching lines @@
           Converter.convertToIceType(FuncType->getParamType(I)));
     }
     FunctionDeclaration *IceFunc = FunctionDeclaration::create(
         Ctx, Signature, Func.getCallingConv(), Func.getLinkage(), Func.empty());
     IceFunc->setName(Func.getName());
     if (!IceFunc->verifyLinkageCorrect(Ctx)) {
       std::string Buffer;
       raw_string_ostream StrBuf(Buffer);
       StrBuf << "Function " << IceFunc->getName()
              << " has incorrect linkage: " << IceFunc->getLinkageName();
+      if (IceFunc->isExternal())
+        StrBuf << "\n  Use flag -allow-externally-defined-symbols to override";
       report_fatal_error(StrBuf.str());
     }
     GlobalDeclarationMap[&Func] = IceFunc;
   }
   // Install global variable declarations.
   for (Module::const_global_iterator I = Mod->global_begin(),
                                      E = Mod->global_end();
        I != E; ++I) {
     const GlobalVariable *GV = I;
     VariableDeclaration *Var = VariableDeclaration::create(Ctx);
     Var->setName(GV->getName());
     Var->setAlignment(GV->getAlignment());
     Var->setIsConstant(GV->isConstant());
     Var->setLinkage(GV->getLinkage());
     if (!Var->verifyLinkageCorrect(Ctx)) {
       std::string Buffer;
       raw_string_ostream StrBuf(Buffer);
       StrBuf << "Global " << Var->getName()
              << " has incorrect linkage: " << Var->getLinkageName();
+      if (Var->isExternal())
+        StrBuf << "\n  Use flag -allow-externally-defined-symbols to override";
       report_fatal_error(StrBuf.str());
     }
     GlobalDeclarationMap[GV] = Var;
   }
 }
 
 void Converter::convertGlobals(Module *Mod) {
   lowerGlobals(LLVM2ICEGlobalsConverter(*this).convertGlobalsToIce(Mod));
 }
 
@@ skipping 10 matching lines @@
       Ctx->pushTimer(TimerID, StackID);
     }
     LLVM2ICEFunctionConverter FunctionConverter(*this);
     FunctionConverter.convertFunction(&I);
     if (TimeThisFunction)
       Ctx->popTimer(TimerID, StackID);
   }
 }
 
 } // end of namespace Ice