[libcxx] Delay evaluation of __make_tuple_types to prevent blowing the max template instantiation depth. Fixes Bug #18345

Summary:
http://llvm.org/bugs/show_bug.cgi?id=18345

Tuple's constructor and assignment operators for "tuple-like" types evaluates __make_tuple_types unnecessarily. In the case of a large array this can blow the template instantiation depth.

Ex:
```
#include <array>
#include <tuple>
#include <memory>
 
typedef std::array<int, 1256> array_t;
typedef std::tuple<array_t> tuple_t;

int main() {
  array_t a;
  tuple_t t(a); // broken
  t = a; // broken

  // make_shared uses tuple behind the scenes. This bug breaks this code.
  std::make_shared<array_t>(a);
}
```

To prevent this from happening we delay the instantiation of `__make_tuple_types` until after we perform the length check. Currently `__make_tuple_types` is instantiated at the same time that the length check .


Test Plan: Two tests have been added. One for the "tuple-like" constructors and another for the "tuple-like" assignment operator. 

Reviewers: mclow.lists, EricWF

Reviewed By: EricWF

Subscribers: K-ballo, cfe-commits

Differential Revision: http://reviews.llvm.org/D4467

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@220769 91177308-0d34-0410-b5e6-96231b3b80d8

test/utilities/tuple/tuple.tuple/tuple.assign/tuple_array_template_depth.pass.cpp

@@ -0,0 +1,32 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// <tuple>
+
+// template <class... Types> class tuple;
+
+// template <class Tuple, __tuple_assignable<Tuple, tuple> >
+//   tuple & operator=(Tuple &&);
+
+// This test checks that we do not evaluate __make_tuple_types
+// on the array when it doesn't match the size of the tuple.
+
+#include <array>
+#include <tuple>
+
+// Use 1256 to try and blow the template instantiation depth for all compilers.
+typedef std::array<char, 1256> array_t;
+typedef std::tuple<array_t> tuple_t;
+
+int main()
+{
+    array_t arr;
+    tuple_t tup;
+    tup = arr;
+}