[libc++] Add #if 0 block to all the top-level headers (#119234)

Including The frozen C++03 headers results in a lot of formatting
changes in the main headers, so this splits these changes into a
separate commit instead.

This is part of
https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc.

libcxx/include/any

@@ -80,41 +80,43 @@ namespace std {
 
 */
 
-#include <__config>
-#include <__memory/allocator.h>
-#include <__memory/allocator_destructor.h>
-#include <__memory/allocator_traits.h>
-#include <__memory/unique_ptr.h>
-#include <__type_traits/add_cv_quals.h>
-#include <__type_traits/add_pointer.h>
-#include <__type_traits/aligned_storage.h>
-#include <__type_traits/conditional.h>
-#include <__type_traits/decay.h>
-#include <__type_traits/enable_if.h>
-#include <__type_traits/is_constructible.h>
-#include <__type_traits/is_function.h>
-#include <__type_traits/is_nothrow_constructible.h>
-#include <__type_traits/is_reference.h>
-#include <__type_traits/is_same.h>
-#include <__type_traits/is_void.h>
-#include <__type_traits/remove_cv.h>
-#include <__type_traits/remove_cvref.h>
-#include <__type_traits/remove_reference.h>
-#include <__utility/forward.h>
-#include <__utility/in_place.h>
-#include <__utility/move.h>
-#include <__utility/unreachable.h>
-#include <__verbose_abort>
-#include <initializer_list>
-#include <typeinfo>
-#include <version>
-
-#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#  pragma GCC system_header
-#endif
+#if 0
+#else // 0
+#  include <__config>
+#  include <__memory/allocator.h>
+#  include <__memory/allocator_destructor.h>
+#  include <__memory/allocator_traits.h>
+#  include <__memory/unique_ptr.h>
+#  include <__type_traits/add_cv_quals.h>
+#  include <__type_traits/add_pointer.h>
+#  include <__type_traits/aligned_storage.h>
+#  include <__type_traits/conditional.h>
+#  include <__type_traits/decay.h>
+#  include <__type_traits/enable_if.h>
+#  include <__type_traits/is_constructible.h>
+#  include <__type_traits/is_function.h>
+#  include <__type_traits/is_nothrow_constructible.h>
+#  include <__type_traits/is_reference.h>
+#  include <__type_traits/is_same.h>
+#  include <__type_traits/is_void.h>
+#  include <__type_traits/remove_cv.h>
+#  include <__type_traits/remove_cvref.h>
+#  include <__type_traits/remove_reference.h>
+#  include <__utility/forward.h>
+#  include <__utility/in_place.h>
+#  include <__utility/move.h>
+#  include <__utility/unreachable.h>
+#  include <__verbose_abort>
+#  include <initializer_list>
+#  include <typeinfo>
+#  include <version>
+
+#  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#    pragma GCC system_header
+#  endif
 
 _LIBCPP_PUSH_MACROS
-#include <__undef_macros>
+#  include <__undef_macros>
 
 namespace std {
 class _LIBCPP_EXPORTED_FROM_ABI _LIBCPP_AVAILABILITY_BAD_ANY_CAST bad_any_cast : public bad_cast {
@@ -125,14 +127,14 @@ public:
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER >= 17
+#  if _LIBCPP_STD_VER >= 17
 
 [[noreturn]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_ANY_CAST void __throw_bad_any_cast() {
-#  if _LIBCPP_HAS_EXCEPTIONS
+#    if _LIBCPP_HAS_EXCEPTIONS
   throw bad_any_cast();
-#  else
+#    else
   _LIBCPP_VERBOSE_ABORT("bad_any_cast was thrown in -fno-exceptions mode");
-#  endif
+#    endif
 }
 
 // Forward declarations
@@ -174,10 +176,10 @@ inline _LIBCPP_HIDE_FROM_ABI constexpr const void* __get_fallback_typeid() {
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool __compare_typeid(type_info const* __id, const void* __fallback_id) {
-#  if _LIBCPP_HAS_RTTI
+#    if _LIBCPP_HAS_RTTI
   if (__id && *__id == typeid(_Tp))
     return true;
-#  endif
+#    endif
   return !__id && __fallback_id == __any_imp::__get_fallback_typeid<_Tp>();
 }
 
@@ -264,15 +266,15 @@ public:
   // 6.3.4 any observers
   _LIBCPP_HIDE_FROM_ABI bool has_value() const _NOEXCEPT { return __h_ != nullptr; }
 
-#  if _LIBCPP_HAS_RTTI
+#    if _LIBCPP_HAS_RTTI
   _LIBCPP_HIDE_FROM_ABI const type_info& type() const _NOEXCEPT {
     if (__h_) {
       return *static_cast<type_info const*>(this->__call(_Action::_TypeInfo));
     } else {
       return typeid(void);
     }
   }
-#  endif
+#    endif
 
 private:
   typedef __any_imp::_Action _Action;
@@ -370,11 +372,11 @@ private:
   }
 
   _LIBCPP_HIDE_FROM_ABI static void* __type_info() {
-#  if _LIBCPP_HAS_RTTI
+#    if _LIBCPP_HAS_RTTI
     return const_cast<void*>(static_cast<void const*>(&typeid(_Tp)));
-#  else
+#    else
     return nullptr;
-#  endif
+#    endif
   }
 };
 
@@ -442,11 +444,11 @@ private:
   }
 
   _LIBCPP_HIDE_FROM_ABI static void* __type_info() {
-#  if _LIBCPP_HAS_RTTI
+#    if _LIBCPP_HAS_RTTI
     return const_cast<void*>(static_cast<void const*>(&typeid(_Tp)));
-#  else
+#    else
     return nullptr;
-#  endif
+#    endif
   }
 };
 
@@ -577,37 +579,38 @@ _LIBCPP_HIDE_FROM_ABI add_pointer_t<_ValueType> any_cast(any* __any) _NOEXCEPT {
     void* __p = __any->__call(
         _Action::_Get,
         nullptr,
-#  if _LIBCPP_HAS_RTTI
+#    if _LIBCPP_HAS_RTTI
         &typeid(_ValueType),
-#  else
+#    else
         nullptr,
-#  endif
+#    endif
         __any_imp::__get_fallback_typeid<_ValueType>());
     return std::__pointer_or_func_cast<_ReturnType>(__p, is_function<_ValueType>{});
   }
   return nullptr;
 }
 
-#endif // _LIBCPP_STD_VER >= 17
+#  endif // _LIBCPP_STD_VER >= 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
-#if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 17
-#  include <chrono>
-#endif
-
-#if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
-#  include <atomic>
-#  include <concepts>
-#  include <cstdlib>
-#  include <iosfwd>
-#  include <iterator>
-#  include <memory>
-#  include <stdexcept>
-#  include <type_traits>
-#  include <variant>
-#endif
+#  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 17
+#    include <chrono>
+#  endif
+
+#  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
+#    include <atomic>
+#    include <concepts>
+#    include <cstdlib>
+#    include <iosfwd>
+#    include <iterator>
+#    include <memory>
+#    include <stdexcept>
+#    include <type_traits>
+#    include <variant>
+#  endif
+#endif // 0
 
 #endif // _LIBCPP_ANY