clang: add support for asmjs arch and Emscripten OS

lib/Driver/ToolChains.h

Index: lib/Driver/ToolChains.h
diff --git a/lib/Driver/ToolChains.h b/lib/Driver/ToolChains.h
index 467072edbc3413ac9dd856d5f877c89f6768e914..7e2be4af297807aa1cafbb5c291d6e5bae0a1471 100644
--- a/lib/Driver/ToolChains.h
+++ b/lib/Driver/ToolChains.h
@@ -715,6 +715,23 @@ public:
   static StringRef GetTargetCPU(const llvm::opt::ArgList &Args);
 };
 
+// @LOCALMOD-START Emscripten
+/// EmscriptenToolChain - A toolchain for the Emscripten C/C++ to JS compiler.
+class LLVM_LIBRARY_VISIBILITY EmscriptenToolChain : public ToolChain {
+public:
+  EmscriptenToolChain(const Driver &D, const llvm::Triple &Triple,
+                      const llvm::opt::ArgList &Args)
+      : ToolChain(D, Triple, Args) {}
+  ~EmscriptenToolChain() override {}
+
+  bool IsMathErrnoDefault() const override { return false; }
+  bool IsObjCNonFragileABIDefault() const override { return true; }
+  bool isPICDefault() const override { return false; }
+  bool isPIEDefault() const override { return false; }
+  bool isPICDefaultForced() const override { return false; }
+};
+// @LOCALMOD-END Emscripten
+
 // @LOCALMOD-START
 class LLVM_LIBRARY_VISIBILITY NaCl_TC : public Generic_ELF {
 public: