Add `REQUIRES: c++experimental` where appropriate.

[danalbert]

Summary

I haven't added it to all the tests, just those that fail without it
(those that aren't header only).

test/libcxx/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/max_size.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // EXTENSION
 // std::size_t polymorphic_allocator<T>::max_size() const noexcept

test/libcxx/experimental/memory/memory.resource.global/global_memory_resource_lifetime.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // memory_resource * new_delete_resource()
 
 // The lifetime of the value returned by 'new_delete_resource()' should
 // never end, even very late into program termination. This test constructs

test/libcxx/experimental/memory/memory.resource.global/new_delete_resource_lifetime.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // memory_resource * new_delete_resource()
 
 // The lifetime of the value returned by 'new_delete_resource()' should
 // never end, even very late into program termination. This test constructs

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.ctor/default.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // polymorphic_allocator<T>::polymorphic_allocator() noexcept
 

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.eq/equal.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator;
 
 // template <class T, class U>
 // bool operator==(

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.eq/not_equal.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator;
 
 // template <class T>
 // bool operator!=(

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/allocate.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // T* polymorphic_allocator<T>::allocate(size_t n)
 

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/construct_pair.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // template <class U1, class U2>
 // void polymorphic_allocator<T>::construct(pair<U1, U2>*)

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/construct_pair_const_lvalue_pair.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // template <class P1, class P2, class U1, class U2>
 // void polymorphic_allocator<T>::construct(pair<P1, P2>*, pair<U1, U2> const&)

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/construct_pair_rvalue.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // template <class P1, class P2, class U1, class U2>
 // void polymorphic_allocator<T>::construct(pair<P1, P2>*, pair<U1, U2> &&)

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/construct_pair_values.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // template <class P1, class P2, class U1, class U2>
 // void polymorphic_allocator<T>::construct(pair<P1, P2>*, U1&&, U2&&)

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/construct_piecewise_pair.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // template <class U1, class U2, class ...Args1, class ...Args2>
 // void polymorphic_allocator<T>::construct(pair<U1, U2>*, piecewise_construct_t

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/construct_types.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // template <class U, class ...Args>
 // void polymorphic_allocator<T>::construct(U *, Args &&...)

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/deallocate.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // T* polymorphic_allocator<T>::deallocate(T*, size_t size)
 

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/destroy.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // template <class U>
 // void polymorphic_allocator<T>::destroy(U * ptr);

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/resource.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // memory_resource *
 // polymorphic_allocator<T>::resource() const

test/std/experimental/memory/memory.polymorphic.allocator.class/memory.polymorphic.allocator.mem/select_on_container_copy_construction.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // template <class T> class polymorphic_allocator
 
 // polymorphic_allocator
 // polymorphic_allocator<T>::select_on_container_copy_construction() const

test/std/experimental/memory/memory.resource.aliases/header_deque_synop.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/deque>
 
 // namespace std { namespace experimental { namespace pmr {
 // template <class T>
 // using deque =
 //     ::std::deque<T, polymorphic_allocator<T>>

test/std/experimental/memory/memory.resource.aliases/header_forward_list_synop.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/forward_list>
 
 // namespace std { namespace experimental { namespace pmr {
 // template <class T>
 // using forward_list =
 //     ::std::forward_list<T, polymorphic_allocator<T>>

test/std/experimental/memory/memory.resource.aliases/header_list_synop.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/list>
 
 // namespace std { namespace experimental { namespace pmr {
 // template <class T>
 // using list =
 //     ::std::list<T, polymorphic_allocator<T>>

test/std/experimental/memory/memory.resource.aliases/header_map_synop.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/map>
 
 // namespace std { namespace experimental { namespace pmr {
 // template <class K, class V, class Compare = less<Key> >
 // using map =
 //     ::std::map<K, V, Compare, polymorphic_allocator<pair<const K, V>>>

test/std/experimental/memory/memory.resource.aliases/header_regex_synop.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/regex>
 
 // namespace std { namespace experimental { namespace pmr {
 //
 //  template <class BidirectionalIterator>
 //  using match_results =

test/std/experimental/memory/memory.resource.aliases/header_set_synop.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/set>
 
 // namespace std { namespace experimental { namespace pmr {
 // template <class V, class Compare = less<V> >
 // using set =
 //     ::std::set<V, Compare, polymorphic_allocator<V>>

test/std/experimental/memory/memory.resource.aliases/header_string_synop.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/string>
 
 // namespace std { namespace experimental { namespace pmr {
 // template <class Char, class Traits = ...>
 // using basic_string =
 //     ::std::basic_string<Char, Traits, polymorphic_allocator<Char>>

test/std/experimental/memory/memory.resource.aliases/header_unordered_map_synop.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/unordered_map>
 
 // namespace std { namespace experimental { namespace pmr {
 // template <class K, class V, class H = hash<K>, class P = equal_to<K> >
 // using unordered_map =
 //     ::std::unordered_map<K, V, H, P, polymorphic_allocator<pair<const K, V>>>

test/std/experimental/memory/memory.resource.aliases/header_unordered_set_synop.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/unordered_set>
 
 // namespace std { namespace experimental { namespace pmr {
 // template <class V, class H = hash<V>, class P = equal_to<V> >
 // using unordered_set =
 //     ::std::unordered_set<V, H, P, polymorphic_allocator<V>>

test/std/experimental/memory/memory.resource.aliases/header_vector_synop.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/vector>
 
 // namespace std { namespace experimental { namespace pmr {
 // template <class T>
 // using vector =
 //     ::std::vector<T, polymorphic_allocator<T>>

test/std/experimental/memory/memory.resource.global/default_resource.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 //-----------------------------------------------------------------------------
 // TESTING memory_resource * get_default_resource() noexcept;
 //         memory_resource * set_default_resource(memory_resource*) noexcept;
 //

test/std/experimental/memory/memory.resource.global/new_delete_resource.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // memory_resource * new_delete_resource()
 
 #include <experimental/memory_resource>
 #include <type_traits>

test/std/experimental/memory/memory.resource.global/null_memory_resource.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: c++experimental
 // UNSUPPORTED: c++98, c++03
 
 // <experimental/memory_resource>
 
 // memory_resource * null_memory_resource()
 
 #include <experimental/memory_resource>
 #include <new>