Expose accidentally removed __compressed_pair constructor taking piecewise_construct_t. This fixes http://llvm.org/bugs/show_bug.cgi?id=15918 .

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@181217 91177308-0d34-0410-b5e6-96231b3b80d8

test/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/alloc_F.pass.cpp

@@ -49,6 +49,11 @@ int A::count = 0;
 
 int g(int) {return 0;}
 
+class Foo {
+public:
+  void bar(int k) { }
+};
+
 int main()
 {
     {
@@ -77,4 +82,9 @@ int main()
     assert(f);
     assert(f.target<int (A::*)(int) const>() != 0);
     }
+    {
+    Foo f;
+    std::function<void(int)> fun = std::bind(&Foo::bar, &f, std::placeholders::_1);
+    fun(10);
+    }
 }