Use LLVM LTO instead of IR types to improve compatibility

lib/Driver/Driver.cpp

 //===--- Driver.cpp - Clang GCC Compatible Driver -------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "clang/Driver/Driver.h"
@@ skipping 1346 matching lines @@
     if (Args.hasArg(options::OPT_module_file_info))
       return llvm::make_unique<CompileJobAction>(std::move(Input),
                                                  types::TY_ModuleFile);
     if (Args.hasArg(options::OPT_verify_pch))
       return llvm::make_unique<VerifyPCHJobAction>(std::move(Input),
                                                    types::TY_Nothing);
     return llvm::make_unique<CompileJobAction>(std::move(Input),
                                                types::TY_LLVM_BC);
   }
   case phases::Backend: {
-    if (IsUsingLTO(TC, Args)) {
+    if (IsUsingLTO(TC, Args) || TC.isBitcodeOnlyTarget()) {
       types::ID Output =
         Args.hasArg(options::OPT_S) ? types::TY_LTO_IR : types::TY_LTO_BC;
       return llvm::make_unique<BackendJobAction>(std::move(Input), Output);
     }
-    if (Args.hasArg(options::OPT_emit_llvm) || TC.isBitcodeOnlyTarget()) {
+    if (Args.hasArg(options::OPT_emit_llvm)) {
       types::ID Output =
         Args.hasArg(options::OPT_S) ? types::TY_LLVM_IR : types::TY_LLVM_BC;
       return llvm::make_unique<BackendJobAction>(std::move(Input), Output);
     }
     return llvm::make_unique<BackendJobAction>(std::move(Input),
                                                types::TY_PP_Asm);
   }
   case phases::Assemble:
     return llvm::make_unique<AssembleJobAction>(std::move(Input),
                                                 types::TY_Object);
@@ skipping 814 matching lines @@
   } else {
     ExcludedFlagsBitmask |= options::CLOption;
   }
 
   return std::make_pair(IncludedFlagsBitmask, ExcludedFlagsBitmask);
 }
 
 bool clang::driver::isOptimizationLevelFast(const llvm::opt::ArgList &Args) {
   return Args.hasFlag(options::OPT_Ofast, options::OPT_O_Group, false);
 }