[libc++] Move AIX and z/OS to the new locale API

This completes the transition of z/OS and AIX to the new locale
base API. I tried my best to make the code 100% equivalent to
the previous code, however it's very difficult to do that without
having access to that platform.

Overall, this makes the locale API definition a lot more direct on
those platforms and also moves in the direction of removing the legacy
shim layer.

Author: ldionne

libcxx/include/CMakeLists.txt

@@ -516,7 +516,6 @@ set(files
   __locale_dir/get_c_locale.h
   __locale_dir/locale_base_api.h
   __locale_dir/locale_base_api/bsd_locale_fallbacks.h
-  __locale_dir/locale_base_api/ibm.h
   __locale_dir/locale_base_api/musl.h
   __locale_dir/locale_base_api/openbsd.h
   __locale_dir/messages.h
@@ -528,6 +527,7 @@ set(files
   __locale_dir/support/bsd_like.h
   __locale_dir/support/freebsd.h
   __locale_dir/support/fuchsia.h
+  __locale_dir/support/ibm.h
   __locale_dir/support/linux.h
   __locale_dir/support/no_locale/characters.h
   __locale_dir/support/no_locale/strtonum.h
@@ -753,7 +753,6 @@ set(files
   __string/constexpr_c_functions.h
   __string/extern_template_lists.h
   __support/ibm/gettod_zos.h
-  __support/ibm/locale_mgmt_zos.h
   __support/ibm/nanosleep.h
   __support/xlocale/__nop_locale_mgmt.h
   __support/xlocale/__posix_l_fallback.h

libcxx/include/__locale_dir/locale_base_api.h

@@ -121,15 +121,15 @@
 #    include <__locale_dir/support/fuchsia.h>
 #  elif defined(__linux__)
 #    include <__locale_dir/support/linux.h>
+#  elif defined(_AIX) || defined(__MVS__)
+#    include <__locale_dir/support/ibm.h>
 #  else
 
 // TODO: This is a temporary definition to bridge between the old way we defined the locale base API
 //       (by providing global non-reserved names) and the new API. As we move individual platforms
 //       towards the new way of defining the locale base API, this should disappear since each platform
 //       will define those directly.
-#    if defined(_AIX) || defined(__MVS__)
-#      include <__locale_dir/locale_base_api/ibm.h>
-#    elif defined(__OpenBSD__)
+#    if defined(__OpenBSD__)
 #      include <__locale_dir/locale_base_api/openbsd.h>
 #    elif defined(__wasi__) || _LIBCPP_HAS_MUSL_LIBC
 #      include <__locale_dir/locale_base_api/musl.h>