clang: add support for asmjs arch and Emscripten OS

lib/Driver/ToolChains.cpp

Index: lib/Driver/ToolChains.cpp
diff --git a/lib/Driver/ToolChains.cpp b/lib/Driver/ToolChains.cpp
index d4281d97c17d62fecc0ac0acbd99ce2096b454c2..adf3a8e6af9b7b24b3a339627d6fac3149f17c08 100644
--- a/lib/Driver/ToolChains.cpp
+++ b/lib/Driver/ToolChains.cpp
@@ -2304,6 +2304,20 @@ StringRef Hexagon_TC::GetTargetCPU(const ArgList &Args)
 }
 // End Hexagon
 
+// @LOCALMOD-START Emscripten
+/// EmscriptenToolChain - A toolchain for the Emscripten C/C++ to JS compiler.
+EmscriptenToolChain::EmscriptenToolChain(const Driver &D,
+                                         const llvm::Triple &Triple,
+                                         const ArgList &Args)
+    : ToolChain(D, Triple, Args) {}
+EmscriptenToolChain::~EmscriptenToolChain() {}
+bool EmscriptenToolChain::IsMathErrnoDefault() const { return false; }
+bool EmscriptenToolChain::IsObjCNonFragileABIDefault() const { return true; }
+bool EmscriptenToolChain::isPICDefault() const { return false; }
+bool EmscriptenToolChain::isPIEDefault() const { return false; }
+bool EmscriptenToolChain::isPICDefaultForced() const { return false; }
+// @LOCALMOD-END Emscripten
+
 // @LOCALMOD-START
 /// NaCl Toolchain
 NaCl_TC::NaCl_TC(const Driver &D, const llvm::Triple &Triple,