clang: add support for asmjs arch and Emscripten OS

lib/CodeGen/ItaniumCXXABI.cpp

 //===------- ItaniumCXXABI.cpp - Emit LLVM Code from ASTs for a Module ----===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This provides C++ code generation targeting the Itanium C++ ABI.  The class
@@ skipping 321 matching lines @@
   case TargetCXXABI::iOS64:
     return new iOS64CXXABI(CGM);
 
   // Note that AArch64 uses the generic ItaniumCXXABI class since it doesn't
   // include the other 32-bit ARM oddities: constructor/destructor return values
   // and array cookies.
   case TargetCXXABI::GenericAArch64:
     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) {
       // For PNaCl, use ARM-style method pointers so that PNaCl code
       // does not assume anything about the alignment of function
       // pointers.
       return new ItaniumCXXABI(CGM, /* UseARMMethodPtrABI = */ true,
                                /* UseARMGuardVarABI = */ false);
     }
     return new ItaniumCXXABI(CGM);
@@ skipping 2844 matching lines @@
     SmallString<256> Buffer;
     llvm::raw_svector_ostream Out(Buffer);
     if (DD)
       getMangleContext().mangleCXXDtorComdat(DD, Out);
     else
       getMangleContext().mangleCXXCtorComdat(CD, Out);
     llvm::Comdat *C = CGM.getModule().getOrInsertComdat(Out.str());
     Fn->setComdat(C);
   }
 }