Fix gcc 5.2 compilation when _GLIBCXX_USE_CXX11_ABI is not 0

Summary: Tested in debian stretch when used in hhvm which can now run drupal 7.
The compilation error is also fixed by #214 but this fix maintains
 forward declarations of basic_string and list.
Closes https://github.com/facebook/folly/pull/329

Reviewed By: yfeldblum

Differential Revision: D2533880

fb-gh-sync-id: 85e18eeeba9efa1b4150217ba526b32b5573e15e

folly/Portability.h

@@ -208,6 +208,16 @@ namespace std { typedef ::max_align_t max_align_t; }
 #define FOLLY_NAMESPACE_STD_END       }
 #endif
 
+// If the new c++ ABI is used, __cxx11 inline namespace needs to be added to
+// some types, e.g. std::list.
+#if _GLIBCXX_USE_CXX11_ABI
+# define FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN _GLIBCXX_BEGIN_NAMESPACE_CXX11
+# define FOLLY_GLIBCXX_NAMESPACE_CXX11_END   _GLIBCXX_END_NAMESPACE_CXX11
+#else
+# define FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
+# define FOLLY_GLIBCXX_NAMESPACE_CXX11_END
+#endif
+
 // Some platforms lack clock_gettime(2) and clock_getres(2). Inject our own
 // versions of these into the global namespace.
 #if FOLLY_HAVE_CLOCK_GETTIME

folly/Traits.h

@@ -240,8 +240,10 @@ FOLLY_NAMESPACE_STD_BEGIN
 template <class T, class U>
   struct pair;
 #ifndef _GLIBCXX_USE_FB
+FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
 template <class T, class R, class A>
   class basic_string;
+FOLLY_GLIBCXX_NAMESPACE_CXX11_END
 #else
 template <class T, class R, class A, class S>
   class basic_string;
@@ -250,8 +252,10 @@ template <class T, class A>
   class vector;
 template <class T, class A>
   class deque;
+FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
 template <class T, class A>
   class list;
+FOLLY_GLIBCXX_NAMESPACE_CXX11_END
 template <class T, class C, class A>
   class set;
 template <class K, class V, class C, class A>