Index: clang/lib/Driver/ToolChains/BareMetal.h
===================================================================
--- clang/lib/Driver/ToolChains/BareMetal.h
+++ clang/lib/Driver/ToolChains/BareMetal.h
@@ -53,7 +53,6 @@
   void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                              llvm::opt::ArgStringList &CC1Args,
                              Action::OffloadKind DeviceOffloadKind) const override;
-  std::string findLibCxxIncludePath(ToolChain::CXXStdlibType LibType) const;
   void AddClangCXXStdlibIncludeArgs(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
Index: clang/lib/Driver/ToolChains/BareMetal.cpp
===================================================================
--- clang/lib/Driver/ToolChains/BareMetal.cpp
+++ clang/lib/Driver/ToolChains/BareMetal.cpp
@@ -95,16 +95,23 @@
   CC1Args.push_back("-nostdsysteminc");
 }
 
-std::string BareMetal::findLibCxxIncludePath(CXXStdlibType LibType) const {
+void BareMetal::AddClangCXXStdlibIncludeArgs(
+    const ArgList &DriverArgs, ArgStringList &CC1Args) const {
+  if (DriverArgs.hasArg(options::OPT_nostdinc) ||
+      DriverArgs.hasArg(options::OPT_nostdlibinc) ||
+      DriverArgs.hasArg(options::OPT_nostdincxx))
+    return;
+
   StringRef SysRoot = getDriver().SysRoot;
   if (SysRoot.empty())
-    return "";
+    return;
 
-  switch (LibType) {
+  switch (GetCXXStdlibType(DriverArgs)) {
   case ToolChain::CST_Libcxx: {
     SmallString<128> Dir(SysRoot);
     llvm::sys::path::append(Dir, "include", "c++", "v1");
-    return Dir.str();
+    addSystemInclude(DriverArgs, CC1Args, Dir.str());
+    break;
   }
   case ToolChain::CST_Libstdcxx: {
     SmallString<128> Dir(SysRoot);
@@ -124,24 +131,12 @@
       Version = CandidateVersion;
     }
     if (Version.Major == -1)
-      return "";
+      return;
     llvm::sys::path::append(Dir, Version.Text);
-    return Dir.str();
+    addSystemInclude(DriverArgs, CC1Args, Dir.str());
+    break;
   }
   }
-  llvm_unreachable("unhandled LibType");
-}
-
-void BareMetal::AddClangCXXStdlibIncludeArgs(
-    const ArgList &DriverArgs, ArgStringList &CC1Args) const {
-  if (DriverArgs.hasArg(options::OPT_nostdinc) ||
-      DriverArgs.hasArg(options::OPT_nostdlibinc) ||
-      DriverArgs.hasArg(options::OPT_nostdincxx))
-    return;
-
-  std::string Path = findLibCxxIncludePath(GetCXXStdlibType(DriverArgs));
-  if (!Path.empty())
-    addSystemInclude(DriverArgs, CC1Args, Path);
 }
 
 void BareMetal::AddCXXStdlibLibArgs(const ArgList &Args,
Index: clang/lib/Driver/ToolChains/CloudABI.h
===================================================================
--- clang/lib/Driver/ToolChains/CloudABI.h
+++ clang/lib/Driver/ToolChains/CloudABI.h
@@ -50,7 +50,9 @@
   GetCXXStdlibType(const llvm::opt::ArgList &Args) const override {
     return ToolChain::CST_Libcxx;
   }
-  std::string findLibCxxIncludePath() const override;
+  void addLibCxxIncludePaths(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override;
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
 
Index: clang/lib/Driver/ToolChains/CloudABI.cpp
===================================================================
--- clang/lib/Driver/ToolChains/CloudABI.cpp
+++ clang/lib/Driver/ToolChains/CloudABI.cpp
@@ -104,10 +104,11 @@
   getFilePaths().push_back(P.str());
 }
 
-std::string CloudABI::findLibCxxIncludePath() const {
+void CloudABI::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
+                                     llvm::opt::ArgStringList &CC1Args) const {
   SmallString<128> P(getDriver().Dir);
   llvm::sys::path::append(P, "..", getTriple().str(), "include/c++/v1");
-  return P.str();
+  addSystemInclude(DriverArgs, CC1Args, P.str());
 }
 
 void CloudABI::AddCXXStdlibLibArgs(const ArgList &Args,
Index: clang/lib/Driver/ToolChains/Contiki.h
===================================================================
--- clang/lib/Driver/ToolChains/Contiki.h
+++ clang/lib/Driver/ToolChains/Contiki.h
@@ -23,7 +23,9 @@
           const llvm::opt::ArgList &Args);
 
   // No support for finding a C++ standard library yet.
-  std::string findLibCxxIncludePath() const override { return ""; }
+  void addLibCxxIncludePaths(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override {}
   void addLibStdCxxIncludePaths(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override {}
Index: clang/lib/Driver/ToolChains/Gnu.h
===================================================================
--- clang/lib/Driver/ToolChains/Gnu.h
+++ clang/lib/Driver/ToolChains/Gnu.h
@@ -316,7 +316,9 @@
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
 
-  virtual std::string findLibCxxIncludePath() const;
+  virtual void
+  addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
+                        llvm::opt::ArgStringList &CC1Args) const;
   virtual void
   addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                            llvm::opt::ArgStringList &CC1Args) const;
Index: clang/lib/Driver/ToolChains/Gnu.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Gnu.cpp
+++ clang/lib/Driver/ToolChains/Gnu.cpp
@@ -2391,12 +2391,9 @@
     return;
 
   switch (GetCXXStdlibType(DriverArgs)) {
-  case ToolChain::CST_Libcxx: {
-    std::string Path = findLibCxxIncludePath();
-    if (!Path.empty())
-      addSystemInclude(DriverArgs, CC1Args, Path);
+  case ToolChain::CST_Libcxx:
+    addLibCxxIncludePaths(DriverArgs, CC1Args);
     break;
-  }
 
   case ToolChain::CST_Libstdcxx:
     addLibStdCxxIncludePaths(DriverArgs, CC1Args);
@@ -2404,9 +2401,12 @@
   }
 }
 
-std::string Generic_GCC::findLibCxxIncludePath() const {
+void
+Generic_GCC::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
+                                   llvm::opt::ArgStringList &CC1Args) const {
   // FIXME: The Linux behavior would probaby be a better approach here.
-  return getDriver().SysRoot + "/usr/include/c++/v1";
+  addSystemInclude(DriverArgs, CC1Args,
+                   getDriver().SysRoot + "/usr/include/c++/v1");
 }
 
 void
Index: clang/lib/Driver/ToolChains/Haiku.h
===================================================================
--- clang/lib/Driver/ToolChains/Haiku.h
+++ clang/lib/Driver/ToolChains/Haiku.h
@@ -27,7 +27,9 @@
     return getTriple().getArch() == llvm::Triple::x86_64;
   }
 
-  std::string findLibCxxIncludePath() const override;
+  void addLibCxxIncludePaths(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override;
   void addLibStdCxxIncludePaths(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
Index: clang/lib/Driver/ToolChains/Haiku.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Haiku.cpp
+++ clang/lib/Driver/ToolChains/Haiku.cpp
@@ -22,8 +22,10 @@
 
 }
 
-std::string Haiku::findLibCxxIncludePath() const {
-  return getDriver().SysRoot + "/system/develop/headers/c++/v1";
+void Haiku::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
+                                  llvm::opt::ArgStringList &CC1Args) const {
+  addSystemInclude(DriverArgs, CC1Args,
+                   getDriver().SysRoot + "/system/develop/headers/c++/v1");
 }
 
 void Haiku::addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
Index: clang/lib/Driver/ToolChains/Lanai.h
===================================================================
--- clang/lib/Driver/ToolChains/Lanai.h
+++ clang/lib/Driver/ToolChains/Lanai.h
@@ -24,7 +24,9 @@
       : Generic_ELF(D, Triple, Args) {}
 
   // No support for finding a C++ standard library yet.
-  std::string findLibCxxIncludePath() const override { return ""; }
+  void addLibCxxIncludePaths(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override {}
   void addLibStdCxxIncludePaths(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override {}
Index: clang/lib/Driver/ToolChains/Linux.h
===================================================================
--- clang/lib/Driver/ToolChains/Linux.h
+++ clang/lib/Driver/ToolChains/Linux.h
@@ -27,7 +27,9 @@
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
-  std::string findLibCxxIncludePath() const override;
+  void addLibCxxIncludePaths(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override;
   void addLibStdCxxIncludePaths(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
Index: clang/lib/Driver/ToolChains/Linux.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Linux.cpp
+++ clang/lib/Driver/ToolChains/Linux.cpp
@@ -775,7 +775,8 @@
   return MaxVersion ? (base + "/" + MaxVersionString).str() : "";
 }
 
-std::string Linux::findLibCxxIncludePath() const {
+void Linux::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
+                                  llvm::opt::ArgStringList &CC1Args) const {
   const std::string LibCXXIncludePathCandidates[] = {
       DetectLibcxxIncludePath(getDriver().Dir + "/../include/c++"),
       // If this is a development, non-installed, clang, libcxx will
@@ -787,9 +788,9 @@
     if (IncludePath.empty() || !getVFS().exists(IncludePath))
       continue;
     // Use the first candidate that exists.
-    return IncludePath;
+    addSystemInclude(DriverArgs, CC1Args, IncludePath);
+    return;
   }
-  return "";
 }
 
 void Linux::addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
Index: clang/lib/Driver/ToolChains/MipsLinux.h
===================================================================
--- clang/lib/Driver/ToolChains/MipsLinux.h
+++ clang/lib/Driver/ToolChains/MipsLinux.h
@@ -31,7 +31,9 @@
 
   CXXStdlibType GetCXXStdlibType(const llvm::opt::ArgList &Args) const override;
 
-  std::string findLibCxxIncludePath() const override;
+  void addLibCxxIncludePaths(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override;
 
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
Index: clang/lib/Driver/ToolChains/MipsLinux.cpp
===================================================================
--- clang/lib/Driver/ToolChains/MipsLinux.cpp
+++ clang/lib/Driver/ToolChains/MipsLinux.cpp
@@ -94,16 +94,18 @@
   return ToolChain::CST_Libcxx;
 }
 
-std::string MipsLLVMToolChain::findLibCxxIncludePath() const {
+void MipsLLVMToolChain::addLibCxxIncludePaths(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args) const {
   if (const auto &Callback = Multilibs.includeDirsCallback()) {
     for (std::string Path : Callback(SelectedMultilib)) {
       Path = getDriver().getInstalledDir() + Path + "/c++/v1";
       if (llvm::sys::fs::exists(Path)) {
-        return Path;
+        addSystemInclude(DriverArgs, CC1Args, Path);
+        return;
       }
     }
   }
-  return "";
 }
 
 void MipsLLVMToolChain::AddCXXStdlibLibArgs(const ArgList &Args,
Index: clang/lib/Driver/ToolChains/Myriad.h
===================================================================
--- clang/lib/Driver/ToolChains/Myriad.h
+++ clang/lib/Driver/ToolChains/Myriad.h
@@ -76,7 +76,9 @@
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
-  std::string findLibCxxIncludePath() const override;
+  void addLibCxxIncludePaths(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override;
   void addLibStdCxxIncludePaths(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
Index: clang/lib/Driver/ToolChains/Myriad.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Myriad.cpp
+++ clang/lib/Driver/ToolChains/Myriad.cpp
@@ -242,9 +242,11 @@
     addSystemInclude(DriverArgs, CC1Args, getDriver().SysRoot + "/include");
 }
 
-std::string MyriadToolChain::findLibCxxIncludePath() const {
+void MyriadToolChain::addLibCxxIncludePaths(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args) const {
   std::string Path(getDriver().getInstalledDir());
-  return Path + "/../include/c++/v1";
+  addSystemInclude(DriverArgs, CC1Args, Path + "/../include/c++/v1");
 }
 
 void MyriadToolChain::addLibStdCxxIncludePaths(
Index: clang/lib/Driver/ToolChains/NaCl.h
===================================================================
--- clang/lib/Driver/ToolChains/NaCl.h
+++ clang/lib/Driver/ToolChains/NaCl.h
@@ -53,7 +53,9 @@
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
-  std::string findLibCxxIncludePath() const override;
+  void addLibCxxIncludePaths(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override;
 
   CXXStdlibType GetCXXStdlibType(const llvm::opt::ArgList &Args) const override;
 
Index: clang/lib/Driver/ToolChains/NaCl.cpp
===================================================================
--- clang/lib/Driver/ToolChains/NaCl.cpp
+++ clang/lib/Driver/ToolChains/NaCl.cpp
@@ -309,25 +309,29 @@
   CmdArgs.push_back("-lc++");
 }
 
-std::string NaClToolChain::findLibCxxIncludePath() const {
+void NaClToolChain::addLibCxxIncludePaths(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args) const {
   const Driver &D = getDriver();
 
   SmallString<128> P(D.Dir + "/../");
   switch (getTriple().getArch()) {
   case llvm::Triple::arm:
     llvm::sys::path::append(P, "arm-nacl/include/c++/v1");
-    return P.str();
+    addSystemInclude(DriverArgs, CC1Args, P.str());
+    break;
   case llvm::Triple::x86:
     llvm::sys::path::append(P, "x86_64-nacl/include/c++/v1");
-    return P.str();
+    addSystemInclude(DriverArgs, CC1Args, P.str());
+    break;
   case llvm::Triple::x86_64:
     llvm::sys::path::append(P, "x86_64-nacl/include/c++/v1");
-    return P.str();
+    addSystemInclude(DriverArgs, CC1Args, P.str());
+    break;
   case llvm::Triple::mipsel:
     llvm::sys::path::append(P, "mipsel-nacl/include/c++/v1");
-    return P.str();
-  default:
-    return "";
+    addSystemInclude(DriverArgs, CC1Args, P.str());
+    break;
   }
 }
 
Index: clang/lib/Driver/ToolChains/NetBSD.h
===================================================================
--- clang/lib/Driver/ToolChains/NetBSD.h
+++ clang/lib/Driver/ToolChains/NetBSD.h
@@ -60,7 +60,9 @@
 
   CXXStdlibType GetDefaultCXXStdlibType() const override;
 
-  std::string findLibCxxIncludePath() const override;
+  void addLibCxxIncludePaths(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override;
   void addLibStdCxxIncludePaths(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
Index: clang/lib/Driver/ToolChains/NetBSD.cpp
===================================================================
--- clang/lib/Driver/ToolChains/NetBSD.cpp
+++ clang/lib/Driver/ToolChains/NetBSD.cpp
@@ -406,8 +406,10 @@
   return ToolChain::CST_Libstdcxx;
 }
 
-std::string NetBSD::findLibCxxIncludePath() const {
-  return getDriver().SysRoot + "/usr/include/c++/";
+void NetBSD::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
+                                   llvm::opt::ArgStringList &CC1Args) const {
+  addSystemInclude(DriverArgs, CC1Args,
+                   getDriver().SysRoot + "/usr/include/c++/");
 }
 
 void NetBSD::addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
Index: clang/lib/Driver/ToolChains/PS4CPU.h
===================================================================
--- clang/lib/Driver/ToolChains/PS4CPU.h
+++ clang/lib/Driver/ToolChains/PS4CPU.h
@@ -61,7 +61,9 @@
          const llvm::opt::ArgList &Args);
 
   // No support for finding a C++ standard library yet.
-  std::string findLibCxxIncludePath() const override { return ""; }
+  void addLibCxxIncludePaths(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override {}
   void addLibStdCxxIncludePaths(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override {}