Index: llvm-toolchain-9-9~+rc3/clang/lib/Driver/ToolChains/Linux.cpp
===================================================================
--- llvm-toolchain-9-9~+rc3.orig/clang/lib/Driver/ToolChains/Linux.cpp
+++ llvm-toolchain-9-9~+rc3/clang/lib/Driver/ToolChains/Linux.cpp
@@ -12,6 +12,7 @@
 #include "Arch/PPC.h"
 #include "Arch/RISCV.h"
 #include "CommonArgs.h"
+#include "clang/Basic/Version.h"
 #include "clang/Config/config.h"
 #include "clang/Driver/Distro.h"
 #include "clang/Driver/Driver.h"
@@ -665,7 +666,16 @@ void Linux::AddClangSystemIncludeArgs(co
   if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<128> P(D.ResourceDir);
     llvm::sys::path::append(P, "include");
-    addSystemInclude(DriverArgs, CC1Args, P);
+    if (llvm::sys::fs::exists(P)) {
+        /* Include the build include directory only
+         * Otherwise, it fails with stage2 when clang headers are available on the system
+         * they usually fail because of the include_next. Two llvm/clang headers are found
+         * while we are waiting for the lib C++ (std or not)
+         */
+        addSystemInclude(DriverArgs, CC1Args, P);
+    } else {
+        addSystemInclude(DriverArgs, CC1Args, "/usr/include/clang/" + std::string(CLANG_VERSION_STRING) + "/include/");
+    }
   }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))