[libc++] Remove experimental pmr headers now shipped in mainline (#73172)

Several experimental headers around std::pmr have been slated for
removal for a while now. This patch actually performs the removal and
cleanups from the code base.

Author: ldionne

libcxx/docs/DesignDocs/ExperimentalFeatures.rst

@@ -106,19 +106,19 @@ Most (but not all) of the features of the LFTS were accepted into C++17.
 +---------+-------------------------------------------------------+--------------------+------------------------------------------+-------------------------+
 | 8.2.2   | ``weak_ptr`` enhancements                             | Not yet            | Never added                              |                         |
 +---------+-------------------------------------------------------+--------------------+------------------------------------------+-------------------------+
-| 8.5     | ``memory_resource``                                   | Not yet            |                                          |                         |
+| 8.5     | ``memory_resource``                                   | 16.0               | 18.0                                     | Removed                 |
 +---------+-------------------------------------------------------+--------------------+------------------------------------------+-------------------------+
-| 8.6     | ``polymorphic_allocator``                             | Not yet            |                                          |                         |
+| 8.6     | ``polymorphic_allocator``                             | 16.0               | 18.0                                     | Removed                 |
 +---------+-------------------------------------------------------+--------------------+------------------------------------------+-------------------------+
 | 8.7     | ``resource_adaptor``                                  |                    | n/a                                      | Not part of C++17       |
 +---------+-------------------------------------------------------+--------------------+------------------------------------------+-------------------------+
-| 8.8     | Access to program-wide ``memory_resource`` objects    | Not yet            |                                          |                         |
+| 8.8     | Access to program-wide ``memory_resource`` objects    | 16.0               | 18.0                                     | Removed                 |
 +---------+-------------------------------------------------------+--------------------+------------------------------------------+-------------------------+
-| 8.9     | Pool resource classes                                 | Not yet            |                                          |                         |
+| 8.9     | Pool resource classes                                 | 16.0               | 18.0                                     | Removed                 |
 +---------+-------------------------------------------------------+--------------------+------------------------------------------+-------------------------+
-| 8.10    | ``monotonic_buffer_resource``                         | Not yet            |                                          |                         |
+| 8.10    | ``monotonic_buffer_resource``                         | 16.0               | 18.0                                     | Removed                 |
 +---------+-------------------------------------------------------+--------------------+------------------------------------------+-------------------------+
-| 8.11    | Alias templates using polymorphic memory resources    | Not yet            |                                          |                         |
+| 8.11    | Alias templates using polymorphic memory resources    | 16.0               | 18.0                                     | Removed                 |
 +---------+-------------------------------------------------------+--------------------+------------------------------------------+-------------------------+
 | 8.12    | Non-owning pointers                                   |                    | n/a                                      | Not part of C++17       |
 +---------+-------------------------------------------------------+--------------------+------------------------------------------+-------------------------+

libcxx/docs/ReleaseNotes/18.rst

@@ -101,17 +101,14 @@ Deprecations and Removals
   Please see the updated documentation about the hardening modes in libc++ and in particular the
   ``_LIBCPP_VERBOSE_ABORT`` macro for details.
 
-Upcoming Deprecations and Removals
-----------------------------------
-
-LLVM 18
-~~~~~~~
-
 - The headers ``<experimental/deque>``, ``<experimental/forward_list>``, ``<experimental/list>``,
   ``<experimental/map>``, ``<experimental/memory_resource>``, ``<experimental/regex>``, ``<experimental/set>``,
   ``<experimental/string>``, ``<experimental/unordered_map>``, ``<experimental/unordered_set>``,
-  and ``<experimental/vector>`` will be removed in LLVM 18, as all their contents will have been implemented in
-  namespace ``std`` for at least two releases.
+  and ``<experimental/vector>`` have been removed in LLVM 18, as all their contents will have been
+  implemented in namespace ``std`` for at least two releases.
+
+Upcoming Deprecations and Removals
+----------------------------------
 
 LLVM 19
 ~~~~~~~

libcxx/include/CMakeLists.txt

@@ -920,23 +920,12 @@ set(files
   experimental/__simd/traits.h
   experimental/__simd/utility.h
   experimental/__simd/vec_ext.h
-  experimental/deque
-  experimental/forward_list
   experimental/iterator
-  experimental/list
-  experimental/map
   experimental/memory
-  experimental/memory_resource
   experimental/propagate_const
-  experimental/regex
-  experimental/set
   experimental/simd
-  experimental/string
   experimental/type_traits
-  experimental/unordered_map
-  experimental/unordered_set
   experimental/utility
-  experimental/vector
   ext/__hash
   ext/hash_map
   ext/hash_set

libcxx/include/__std_clang_module

@@ -86,25 +86,12 @@
 #include <exception>
 #include <execution>
 #include <expected>
-#include <experimental/deque>
-#include <experimental/forward_list>
 #include <experimental/iterator>
-#include <experimental/list>
-#include <experimental/map>
 #include <experimental/memory>
-#include <experimental/memory_resource>
 #include <experimental/propagate_const>
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <experimental/regex>
-#endif
-#include <experimental/set>
 #include <experimental/simd>
-#include <experimental/string>
 #include <experimental/type_traits>
-#include <experimental/unordered_map>
-#include <experimental/unordered_set>
 #include <experimental/utility>
-#include <experimental/vector>
 #include <fenv.h>
 #include <filesystem>
 #include <float.h>

libcxx/include/experimental/__config

@@ -28,10 +28,6 @@
 #define _LIBCPP_END_NAMESPACE_LFTS_V2  } } }
 #define _VSTD_LFTS_V2 _VSTD_EXPERIMENTAL::fundamentals_v2
 
-#define _LIBCPP_BEGIN_NAMESPACE_LFTS_PMR _LIBCPP_BEGIN_NAMESPACE_LFTS namespace pmr {
-#define _LIBCPP_END_NAMESPACE_LFTS_PMR _LIBCPP_END_NAMESPACE_LFTS }
-#define _VSTD_LFTS_PMR _VSTD_LFTS::pmr
-
 // TODO: support more targets
 #if defined(__AVX__)
 #define _LIBCPP_NATIVE_SIMD_WIDTH_IN_BYTES 32