Replace a usage of C++14 language features with C++11 code (#1833)

include/pybind11/functional.h

@@ -65,12 +65,19 @@ public:
             }
         };
 
-        value = [hfunc = func_handle(std::move(func))](Args... args) -> Return {
+        // to emulate 'move initialization capture' in C++11
+        struct func_wrapper {
+            func_handle hfunc;
+            func_wrapper(func_handle&& hf): hfunc(std::move(hf)) {}
+            Return operator()(Args... args) const {
                 gil_scoped_acquire acq;
                 object retval(hfunc.f(std::forward<Args>(args)...));
                 /* Visual studio 2015 parser issue: need parentheses around this expression */
                 return (retval.template cast<Return>());
+            }
         };
+
+        value = func_wrapper(func_handle(std::move(func)));
         return true;
     }