This reverts commit c861fe8a71e64f3d2108c58147e7375cd9314521.

Unfortunately, this use of hidden visibility attributes causes
user-defined specializations of standard-library types to also be marked
hidden by default, which is incorrect. See discussion thread on #131156.

...and also reverts the follow-up commits:

Revert "[libc++] Add explicit ABI annotations to functions from the block runtime declared in <__functional/function.h> (#140592)"
This reverts commit 3e4c9dc299c35155934688184319d391b298fff7.

Revert "[libc++] Make ABI annotations explicit for windows-specific code (#140507)"
This reverts commit f73287e623a6c2e4a3485832bc3e10860cd26eb5.

Revert "[libc++][NFC] Replace a few "namespace std" with the correct macro (#140510)"
This reverts commit 1d411f27c769a32cb22ce50b9dc4421e34fd40dd.

This patch introduces `_LIBCPP_{BEGIN,END}_EXPLICIT_ABI_ANNOTATIONS`,
which allow us to have implicit annotations for most functions, and just
where it's not "hide_from_abi everything" we add explicit annotations.
This allows us to drop the `_LIBCPP_HIDE_FROM_ABI` macro from most
functions in libc++.

Adds missing includes that were detected when I tried to build libc++ as
a module.

Working towards #127012

This is technically not necessary in most cases to prevent issues with ADL,
but let's be consistent. This allows us to remove the libcpp-qualify-declval
clang-tidy check, which is now enforced by the robust-against-adl clang-tidy check.

This macro is deprecated in C++26.

Fixes https://github.com/llvm/llvm-project/issues/81360

---------

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

Implements:
- LWG3869 Deprecate std::errc constants related to UNIX STREAMS

This patch runs clang-format on all of libcxx/include and libcxx/src, in
accordance with the RFC discussed at [1]. Follow-up patches will format
the benchmarks, the test suite and remaining parts of the code. I'm
splitting this one into its own patch so the diff is a bit easier to
review.

This patch was generated with:

   find libcxx/include libcxx/src -type f \
      | grep -v 'module.modulemap.in' \
      | grep -v 'CMakeLists.txt' \
      | grep -v 'README.txt' \
      | grep -v 'libcxx.imp' \
      | grep -v '__config_site.in' \
      | xargs clang-format -i

A Git merge driver is available in libcxx/utils/clang-format-merge-driver.sh
to help resolve merge and rebase issues across these formatting changes.

[1]: https://discourse.llvm.org/t/rfc-clang-formatting-all-of-libc-once-and-for-all

This was contributed ~10 years ago, but we don't officially support it
and I am not aware of any bot testing it, so this has likely rotten to
the point where it is unusable.

Differential Revision: https://reviews.llvm.org/D138680