When localization is disabled, we used to skip testing a lot of headers.
However, these headers are now "no-ops" when localization is disabled,
so they can actually be included. As such, we should test their
inclusion in our usual header inclusion tests.

Co-authored-by: Louis Dionne <ldionne.2@gmail.com>

This is a follow-up to #89178. This updates the `<__config_site>`
macros.

Around half of the tests are based on the tests Arthur O'Dwyer's
original implementation of std::flat_map, with modifications and
removals.

partially implement #105190

Currently, the library-internal feature test macros are only defined if
the feature is not available, and always have the prefix
`_LIBCPP_HAS_NO_`. This patch changes that, so that they are always
defined and have the prefix `_LIBCPP_HAS_` instead. This changes the
canonical use of these macros to `#if _LIBCPP_HAS_FEATURE`, which means
that using an undefined macro (e.g. due to a missing include) is
diagnosed now. While this is rather unlikely currently, a similar change
in `<__configuration/availability.h>` caught a few bugs. This also
improves readability, since it removes the double-negation of `#ifndef
_LIBCPP_HAS_NO_FEATURE`.

The current patch only touches the macros defined in `<__config>`. If
people are happy with this approach, I'll make a follow-up PR to also
change the macros defined in `<__config_site>`.

Instead, make the headers empty like we do for all the other carve-outs.

The _LIBCPP_HAS_NO_THREADS carve-out does not result in hard errors
anymore, but the patch that changed that forgot to update the header
restrictions we use to auto-generate several files.

We can also remove the restrictions for the no-localization build and
no-wide-characters, but doing it is less straightforward so I'm leaving
it out of this patch.

This updates:
- The status tables
- Feature test macros
- New headers for modules

After applying the review comments of
https://github.com/llvm/llvm-project/pull/80478
I've forgotten to update the generated files. This fixes the issue and
removes trailing whitespace.

On Windows the libc++ test suite sees the MSVC STL headers and may
conclude these are libc++ headers when inspecting the name. Modules
guard against forgetting to export new headers. Finding MSVC STL's
headers gives false positives. Since the CI tests non-Windows platforms
too, the validation will be disabled on Windows.

Fixes: https://github.com/llvm/llvm-project/issues/79010

---------

Co-authored-by: Louis Dionne <ldionne.2@gmail.com>