Fix stubs

1. Removed body of `template <class F> function(F&& f)` to avoid type clashes.
2. Copied member declarations of std::allocator from `memory.h` to
`string` to avoid undefined symbol issues.

Author: jeongsoolee09

cpp/common/test/includes/standard-library/functional.h

@@ -89,10 +89,8 @@ template <class> class function;
 template <class R, class... Args> class function<R(Args...)> {
 public:
   function();
-  template <class F> function(F&& f) {
-    auto fptr = new F(std::forward<F>(f));
-  }
+  template <class F> function(F&& f);
   template <class F> function &operator=(F &&);
 };
 } // namespace std
-#endif
+#endif

cpp/common/test/includes/standard-library/string

@@ -88,7 +88,25 @@ template <> struct char_traits<wchar_t> {
   static int_type eof();
 };
 
-template <class T> class allocator;
+template <typename T1> struct allocator {
+  using value_type = T1;
+  using size_type = std::size_t;
+  using difference_type = std::ptrdiff_t;
+
+  constexpr allocator() noexcept = default;
+  constexpr allocator(const allocator &) noexcept = default;
+
+  template <typename T2> constexpr allocator(const allocator<T2> &) noexcept;
+
+  ~allocator() = default;
+
+  T1 *allocate(std::size_t);
+  void deallocate(T1 *, std::size_t);
+};
+
+template <> struct allocator<void> {
+  using value_type = void;
+};
 
 template <class charT, class traits = char_traits<charT>,
           class Allocator = allocator<charT>>
@@ -329,4 +347,4 @@ long double stold(const string &str, size_t *idx = 0);
 std::string to_string(int value);
 } // namespace std
 
-#endif // _GHLIBCPP_STRING
+#endif // _GHLIBCPP_STRING