Fix bind by making _is_valid_bind_return more robust.  It should return false instead of give a compile time error, always.  The problem was down in ____mu_return, the version that handles nested bind objects.  This fixes http://llvm.org/bugs/show_bug.cgi?id=16343

llvm-svn: 185289
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 9bf42533b7d8db7f7b0b44ad8ba28a4d0e15ab08
diff --git a/include/functional b/include/functional
index 995db56..d9e6ee9 100644
--- a/include/functional
+++ b/include/functional
@@ -1594,12 +1594,24 @@
           class _TupleUj>
 struct ____mu_return;
 
+template <bool _Invokable, class _Ti, class ..._Uj>
+struct ____mu_return_invokable  // false
+{
+    typedef __nat type;
+};
+
 template <class _Ti, class ..._Uj>
-struct ____mu_return<_Ti, false, true, false, tuple<_Uj...> >
+struct ____mu_return_invokable<true, _Ti, _Uj...>
 {
     typedef typename __invoke_of<_Ti&, _Uj...>::type type;
 };
 
+template <class _Ti, class ..._Uj>
+struct ____mu_return<_Ti, false, true, false, tuple<_Uj...> >
+    : public ____mu_return_invokable<__invokable<_Ti&, _Uj...>::value, _Ti, _Uj...>
+{
+};
+
 template <class _Ti, class _TupleUj>
 struct ____mu_return<_Ti, false, false, true, _TupleUj>
 {