Index: llvm-toolchain-9_9~+20191120040145+0f34f1b9318/clang/lib/Driver/ToolChains/Linux.cpp
===================================================================
--- llvm-toolchain-9_9~+20191120040145+0f34f1b9318.orig/clang/lib/Driver/ToolChains/Linux.cpp
+++ llvm-toolchain-9_9~+20191120040145+0f34f1b9318/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"
@@ -661,8 +662,18 @@ void Linux::AddClangSystemIncludeArgs(co
   SmallString<128> ResourceDirInclude(D.ResourceDir);
   llvm::sys::path::append(ResourceDirInclude, "include");
   if (!DriverArgs.hasArg(options::OPT_nobuiltininc) &&
-      (!getTriple().isMusl() || DriverArgs.hasArg(options::OPT_nostdlibinc)))
-    addSystemInclude(DriverArgs, CC1Args, ResourceDirInclude);
+      (!getTriple().isMusl() || DriverArgs.hasArg(options::OPT_nostdlibinc))) {
+    if (llvm::sys::fs::exists(ResourceDirInclude)) {
+        /* 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, ResourceDirInclude);
+    } else {
+        addSystemInclude(DriverArgs, CC1Args, "/usr/include/clang/" + std::string(CLANG_VERSION_STRING) + "/include/");
+    }
+  }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;