Index: llvm-toolchain-14-14.0.6/clang/lib/Driver/ToolChains/WebAssembly.cpp
===================================================================
--- llvm-toolchain-14-14.0.6.orig/clang/lib/Driver/ToolChains/WebAssembly.cpp
+++ llvm-toolchain-14-14.0.6/clang/lib/Driver/ToolChains/WebAssembly.cpp
@@ -16,6 +16,7 @@
 #include "clang/Driver/Options.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Option/ArgList.h"
 
 using namespace clang::driver;
@@ -172,7 +173,7 @@ WebAssembly::WebAssembly(const Driver &D
 
   getProgramPaths().push_back(getDriver().getInstalledDir());
 
-  auto SysRoot = getDriver().SysRoot;
+  std::string SysRoot = computeSysRoot();
   if (getTriple().getOS() == llvm::Triple::UnknownOS) {
     // Theoretically an "unknown" OS should mean no standard libraries, however
     // it could also mean that a custom set of libraries is in use, so just add
@@ -396,6 +397,7 @@ void WebAssembly::AddClangSystemIncludeA
     return;
 
   const Driver &D = getDriver();
+  std::string SysRoot = computeSysRoot();
 
   if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<128> P(D.ResourceDir);
@@ -419,27 +421,39 @@ void WebAssembly::AddClangSystemIncludeA
     return;
   }
 
+  // add the multiarch path on e.g. wasm32-wasi
   if (getTriple().getOS() != llvm::Triple::UnknownOS) {
     const std::string MultiarchTriple =
-        getMultiarchTriple(D, getTriple(), D.SysRoot);
-    addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/include/" + MultiarchTriple);
+        getMultiarchTriple(D, getTriple(), SysRoot);
+    addSystemInclude(DriverArgs, CC1Args, SysRoot + "/local/include/" + MultiarchTriple);
+    addSystemInclude(DriverArgs, CC1Args, SysRoot + "/local/include");
+    addSystemInclude(DriverArgs, CC1Args, SysRoot + "/include/" + MultiarchTriple);
   }
-  addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/include");
+
+  // also add the non-multiarch path, only on a known OS (as above), or when
+  // a sysroot is given, for backwards compatibility with the original driver
+  if (getTriple().getOS() != llvm::Triple::UnknownOS ||
+      !getDriver().SysRoot.empty())
+    addSystemInclude(DriverArgs, CC1Args, SysRoot + "/include");
 }
 
 void WebAssembly::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
                                                ArgStringList &CC1Args) const {
+  std::string SysRoot = computeSysRoot();
+
   if (!DriverArgs.hasArg(options::OPT_nostdlibinc) &&
       !DriverArgs.hasArg(options::OPT_nostdincxx)) {
     if (getTriple().getOS() != llvm::Triple::UnknownOS) {
       const std::string MultiarchTriple =
-          getMultiarchTriple(getDriver(), getTriple(), getDriver().SysRoot);
+          getMultiarchTriple(getDriver(), getTriple(), SysRoot);
       addSystemInclude(DriverArgs, CC1Args,
-                       getDriver().SysRoot + "/include/" + MultiarchTriple +
+                       SysRoot + "/include/" + MultiarchTriple +
                            "/c++/v1");
     }
-    addSystemInclude(DriverArgs, CC1Args,
-                     getDriver().SysRoot + "/include/c++/v1");
+
+    // don't include the host architecture's headers in the search path
+    if (!getDriver().SysRoot.empty())
+      addSystemInclude(DriverArgs, CC1Args, SysRoot + "/include/c++/v1");
   }
 }
 
@@ -467,3 +481,15 @@ SanitizerMask WebAssembly::getSupportedS
 Tool *WebAssembly::buildLinker() const {
   return new tools::wasm::Linker(*this);
 }
+
+std::string WebAssembly::computeSysRoot() const {
+  if (!getDriver().SysRoot.empty())
+    return getDriver().SysRoot;
+
+  std::string Path = "/usr";
+  if (getVFS().exists(Path))
+    return Path;
+
+  return std::string();
+}
+
Index: llvm-toolchain-14-14.0.6/clang/lib/Driver/ToolChains/WebAssembly.h
===================================================================
--- llvm-toolchain-14-14.0.6.orig/clang/lib/Driver/ToolChains/WebAssembly.h
+++ llvm-toolchain-14-14.0.6/clang/lib/Driver/ToolChains/WebAssembly.h
@@ -80,6 +80,8 @@ private:
   std::string getMultiarchTriple(const Driver &D,
                                  const llvm::Triple &TargetTriple,
                                  StringRef SysRoot) const override;
+
+  std::string computeSysRoot() const override;
 };
 
 } // end namespace toolchains