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

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

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>

Let the std.compat module use the std module instead of duplicating the
exports.

Based on @ChuanqiXu9's suggestion in #71438.

This adds the std.compat module. The patch contains a bit of refactoring
to avoid code duplication between the std and std.compat module.

Implements parts of
- P2465R3 Standard Library Modules std and std.compat