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

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@185289 91177308-0d34-0410-b5e6-96231b3b80d8

test/utilities/function.objects/bind/func.bind/func.bind.bind/nested.pass.cpp

@@ -0,0 +1,51 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <functional>
+
+// template<CopyConstructible Fn, CopyConstructible... Types>
+//   unspecified bind(Fn, Types...);
+// template<Returnable R, CopyConstructible Fn, CopyConstructible... Types>
+//   unspecified bind(Fn, Types...);
+
+// http://llvm.org/bugs/show_bug.cgi?id=16343
+
+#include <cmath>
+#include <functional>
+#include <cassert>
+
+struct power
+{
+  template <typename T>
+  T
+  operator()(T a, T b)
+  {
+    return std::pow(a, b);
+  }
+};
+
+struct plus_one
+{
+  template <typename T>
+  T
+  operator()(T a)
+  {
+    return a + 1;
+  }
+};
+
+int
+main()
+{
+    using std::placeholders::_1;
+
+    auto g = std::bind(power(), 2, _1);
+    assert(g(5) == 32);
+    assert(std::bind(plus_one(), g)(5) == 33);
+}