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

Revert "Fix initialization of array<const T, 0> with GCC."
Revert "Make array<const T, 0> non-CopyAssignable and make swap and fill ill-formed."

This reverts commit r324182, r324185, and r324194 which were causing issues with zero-length std::arrays.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@324309 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/containers/sequences/array/array.swap/swap.fail.cpp

@@ -1,30 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-//                     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.
-//
-//===----------------------------------------------------------------------===//
-
-// <array>
-
-// void swap(array& a);
-
-#include <array>
-#include <cassert>
-
-// std::array is explicitly allowed to be initialized with A a = { init-list };.
-// Disable the missing braces warning for this reason.
-#include "disable_missing_braces_warning.h"
-
-int main() {
-  {
-    typedef double T;
-    typedef std::array<const T, 0> C;
-    C c = {};
-    C c2 = {};
-    // expected-error@array:* {{static_assert failed "cannot swap zero-sized array of type 'const T'"}}
-    c.swap(c2); // expected-note {{requested here}}
-  }
-}