fix emscripten dependencies by making separate test crate

lib/emscripten-tests/emtests/test_exceptions_2.cpp

@@ -0,0 +1,23 @@
+// Copyright 2017 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 <stdexcept>
+#include <stdio.h>
+
+typedef void (*FuncPtr)();
+
+void ThrowException() { throw std::runtime_error("catch me!"); }
+
+FuncPtr ptr = ThrowException;
+
+int main() {
+  try {
+    ptr();
+  }
+  catch (...) {
+    printf("Exception caught successfully!\n");
+  }
+  return 0;
+}