fix emscripten dependencies by making separate test crate

lib/emscripten-tests/emtests/test_exceptions_refcount.cpp

@@ -0,0 +1,25 @@
+// Copyright 2014 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 <exception>
+
+class MyException : public std::exception {
+public:
+  MyException() { printf("me now!\n"); }
+  ~MyException() _NOEXCEPT { printf("i'm over!\n"); }
+};
+
+int main() {
+  {
+    const std::exception_ptr p;
+  }
+  {
+    MyException m;
+  }
+  printf("ok.\n");
+  return 0;
+}
+