Remove Emscripten support

lib/Target/JSBackend/JS.h

-//===-- JS.h - Top-level interface for JS representation ------*- C++ -*-===//
-//
-//                     The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This file contains the entry points for global functions defined in the JS
-// target library, as used by the LLVM JIT.
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef TARGET_JS_H
-#define TARGET_JS_H
-
-namespace llvm {
-
-class ImmutablePass;
-class JSTargetMachine;
-
-/// createJSISelDag - This pass converts a legalized DAG into a
-/// \brief Creates an JS-specific Target Transformation Info pass.
-ImmutablePass *createJSTargetTransformInfoPass(const JSTargetMachine *TM);
-
-} // End llvm namespace
-
-#endif