clang: add support for asmjs arch and Emscripten OS

lib/CodeGen/ItaniumCXXABI.cpp

Index: lib/CodeGen/ItaniumCXXABI.cpp
diff --git a/lib/CodeGen/ItaniumCXXABI.cpp b/lib/CodeGen/ItaniumCXXABI.cpp
index fd299d14c13cffea7be8756e695229e3c99d9553..66743d28546d56193568a2e23fc1d0c89fbd13c2 100644
--- a/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/lib/CodeGen/ItaniumCXXABI.cpp
@@ -339,6 +339,14 @@ CodeGen::CGCXXABI *CodeGen::CreateItaniumCXXABI(CodeGenModule &CGM) {
     return new ItaniumCXXABI(CGM, /* UseARMMethodPtrABI = */ true,
                              /* UseARMGuardVarABI = */ true);
 
+  // @LOCALMOD-START Emscripten
+  case TargetCXXABI::Emscripten:
+    // Use ARM-style method pointers so that generated code does not assume
+    // anything about the alignment of function pointers.
+    return new ItaniumCXXABI(CGM, /* UseARMMethodPtrABI = */ true,
+                             /* UseARMGuardVarABI = */ false);
+  // @LOCALMOD-END Emscripten
+
   case TargetCXXABI::GenericItanium:
     if (CGM.getContext().getTargetInfo().getTriple().getArch()
         == llvm::Triple::le32) {