[libc++] Guard additional headers with _LIBCPP_HAS_LOCALIZATION (llvm#131921)

There were some remaining headers that were not guarded with
_LIBCPP_HAS_LOCALIZATION, leading to errors when trying to use modules
on platforms that don't support localization (since all the headers get
pulled in when building the 'std' module). This patch brings these
headers in line with what we do for every other header that depends on
localization.

This patch also requires including <picolibc.h> from
<__configuration/platform.h> in order to define _NEWLIB_VERSION. In the
long term, we should use a better approach for doing that, such as
defining a macro in the __config_site header.

Author: ldionne

libcxx/include/__configuration/platform.h

@@ -42,6 +42,13 @@
 #  endif
 #endif
 
+// This is required in order for _NEWLIB_VERSION to be defined in places where we use it.
+// TODO: We shouldn't be including arbitrarily-named headers from libc++ since this can break valid
+//       user code. Move code paths that need _NEWLIB_VERSION to another customization mechanism.
+#if __has_include(<picolibc.h>)
+#  include <picolibc.h>
+#endif
+
 #ifndef __BYTE_ORDER__
 #  error                                                                                                               \
       "Your compiler doesn't seem to define __BYTE_ORDER__, which is required by libc++ to know the endianness of your target platform"