[libc++] Fix PR35491 - std::array of zero-size doesn't work with non-default constructible types.

Summary:
This patch fixes llvm.org/PR35491 and LWG2157  (https://cplusplus.github.io/LWG/issue2157)

The fix attempts to maintain ABI compatibility by replacing the array with a instance of `aligned_storage`.

Reviewers: mclow.lists, EricWF

Reviewed By: EricWF

Subscribers: lichray, cfe-commits

Differential Revision: https://reviews.llvm.org/D41223

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@324182 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/containers/sequences/array/begin.pass.cpp

@@ -31,4 +31,13 @@ int main()
         *i = 5.5;
         assert(c[0] == 5.5);
     }
+    {
+      struct NoDefault {
+        NoDefault(int) {}
+      };
+      typedef NoDefault T;
+      typedef std::array<T, 0> C;
+      C c = {};
+      assert(c.begin() == c.end());
+    }
 }