Remove Emscripten support

lib/Target/JSBackend/MCTargetDesc/JSBackendMCTargetDesc.cpp

-//===-- JSBackendMCTargetDesc.cpp - JS Backend Target Descriptions --------===//
-//
-//                     The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This file provides asm.js specific target descriptions.
-//
-//===----------------------------------------------------------------------===//
-
-#include "JSBackendMCTargetDesc.h"
-#include "llvm/MC/MCCodeGenInfo.h"
-#include "llvm/Support/TargetRegistry.h"
-using namespace llvm;
-
-static MCCodeGenInfo *createJSBackendMCCodeGenInfo(StringRef Triple, Reloc::Model RM,
-                                                   CodeModel::Model CM,
-                                                   CodeGenOpt::Level OL) {
-  MCCodeGenInfo *X = new MCCodeGenInfo();
-  X->InitMCCodeGenInfo(RM, CM, OL);
-  return X;
-}
-
-// Force static initialization.
-extern "C" void LLVMInitializeJSBackendTargetMC() {
-  // Register the MC codegen info.
-  RegisterMCCodeGenInfoFn C(TheJSBackendTarget, createJSBackendMCCodeGenInfo);
-}