Index: clang/lib/Driver/ToolChains/WebAssembly.cpp
===================================================================
--- clang/lib/Driver/ToolChains/WebAssembly.cpp
+++ clang/lib/Driver/ToolChains/WebAssembly.cpp
@@ -17,6 +17,7 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Option/ArgList.h"
+#include "llvm/Support/VirtualFileSystem.h"
 
 using namespace clang::driver;
 using namespace clang::driver::tools;
@@ -334,7 +335,11 @@
 WebAssembly::GetCXXStdlibType(const ArgList &Args) const {
   if (Arg *A = Args.getLastArg(options::OPT_stdlib_EQ)) {
     StringRef Value = A->getValue();
-    if (Value != "libc++")
+    if (Value == "libc++")
+        return ToolChain::CST_Libcxx;
+    else if(Value == "libstdc++")
+        return ToolChain::CST_Libstdcxx;
+    else
       getDriver().Diag(diag::err_drv_invalid_stdlib_name)
           << A->getAsString(Args);
   }
@@ -380,17 +385,48 @@
 
 void WebAssembly::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
                                                ArgStringList &CC1Args) const {
-  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);
-      addSystemInclude(DriverArgs, CC1Args,
-                       getDriver().SysRoot + "/include/" + MultiarchTriple +
-                           "/c++/v1");
+  if (DriverArgs.hasArg(options::OPT_nostdinc) ||
+      DriverArgs.hasArg(options::OPT_nostdlibinc) ||
+      DriverArgs.hasArg(options::OPT_nostdincxx))
+    return;
+  SmallString<128> Dir{getDriver().SysRoot};
+  const std::string MultiarchTriple =
+      getMultiarchTriple(getDriver(), getTriple(), getDriver().SysRoot);
+  llvm::sys::path::append(Dir, "include");
+  switch (GetCXXStdlibType(DriverArgs)) {
+  case ToolChain::CST_Libcxx: {
+    SmallString<128> native{Dir};
+    llvm::sys::path::append(native, "c++", "v1");
+    addSystemInclude(DriverArgs, CC1Args, native);
+    llvm::sys::path::append(Dir, MultiarchTriple, "c++", "v1");
+    addSystemInclude(DriverArgs, CC1Args, Dir);
+    break;
+  }
+  case ToolChain::CST_Libstdcxx: {
+    llvm::sys::path::append(Dir, "c++");
+    std::error_code EC;
+    Generic_GCC::GCCVersion Version = {"", -1, -1, -1, "", "", ""};
+    // Walk the subdirs, and find the one with the newest gcc version:
+    for (llvm::vfs::directory_iterator
+             LI = getVFS().dir_begin(Dir.str(), EC),
+             LE;
+         !EC && LI != LE; LI = LI.increment(EC)) {
+      StringRef VersionText = llvm::sys::path::filename(LI->path());
+      auto CandidateVersion = Generic_GCC::GCCVersion::Parse(VersionText);
+      if (CandidateVersion.Major == -1)
+        continue;
+      if (CandidateVersion <= Version)
+        continue;
+      Version = CandidateVersion;
     }
-    addSystemInclude(DriverArgs, CC1Args,
-                     getDriver().SysRoot + "/include/c++/v1");
+    if (Version.Major == -1)
+      return;
+    llvm::sys::path::append(Dir, Version.Text);
+    addSystemInclude(DriverArgs, CC1Args, Dir);
+    llvm::sys::path::append(Dir, MultiarchTriple);
+    addSystemInclude(DriverArgs, CC1Args, Dir);
+    break;
+  }
   }
 }
 
@@ -403,6 +439,10 @@
     CmdArgs.push_back("-lc++abi");
     break;
   case ToolChain::CST_Libstdcxx:
+    CmdArgs.push_back("-lsupc++");
+    CmdArgs.push_back("-lstdc++");
+    break;
+  default:
     llvm_unreachable("invalid stdlib name");
   }
 }