Isolated emscripten in new lib

lib/emscripten/emtests/test_em_asm_unused_arguments.cpp

@@ -0,0 +1,15 @@
+// Copyright 2018 The Emscripten Authors.  All rights reserved.
+// Emscripten is available under two separate licenses, the MIT license and the
+// University of Illinois/NCSA Open Source License.  Both these licenses can be
+// found in the LICENSE file.
+
+#include <stdio.h>
+#include <emscripten.h>
+
+int main(int argc, char **argv) {
+  int sum = EM_ASM_INT({
+     return $0 + $2;
+  }, 0, 1, 2);
+  printf("0+2=%d\n", sum);
+  return 0;
+}