[libcxx] Handle windows system error code mapping in std::error_code. (#93101)

The `std::error_code`/`std::error_category` functionality is designed to
support multiple error domains. On Unix, both

[libcxx] Handle windows system error code mapping in std::error_code. (#93101)

The `std::error_code`/`std::error_category` functionality is designed to
support multiple error domains. On Unix, both system calls and libc
functions return the same error codes, and thus, libc++ today treats
`generic_category()` and `system_category()` as being equivalent.

However, on Windows, libc functions return `errno.h` error codes in the
`errno` global, but system calls return the very different `winerror.h`
error codes via `GetLastError()`.

As such, there is a need to map the winerror.h error codes into generic
errno codes. In libc++, however, the system_error facility does not
implement this mapping; instead the mapping is hidden inside libc++,
used directly by the std::filesystem implementation.

That has a few problems:

1. For std::filesystem APIs, the concrete windows error number is lost,
before users can see it. The intent of the distinction between
std::error_code and std::error_condition is that the error_code return
has the original (potentially more detailed) error code.

2. User-written code which calls Windows system APIs requires this same
mapping, so it also can also return error_code objects that other
(cross-platform) code can understand.

After this commit, an `error_code` with `generic_category()` is used to
report an error from `errno`, and, on Windows only, an `error_code` with
`system_category()` is used to report an error from `GetLastError()`. On
Unix, system_category remains identity-mapped to generic_category, but
is never used by libc++ itself.

The windows error code mapping is moved into system_error, so that
conversion of an `error_code` to `error_condition` correctly translates
the `system_category()` code into a `generic_category()` code, when
appropriate.

This allows code like:
`error_code(GetLastError(), system_category()) == errc::invalid_argument`
to work as expected -- as it does with MSVC STL.

(Continued from old phabricator review [D151493](https://reviews.llvm.org/D151493))

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[libc++] Refactor the configuration macros to being always defined (#112094)

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

[libc++][print] Moves is_terminal to the dylib. (#80464)

Having the test in the header requires including unistd.h on POSIX
platforms. This header has other declarations which may conflict with
co

[libc++][print] Moves is_terminal to the dylib. (#80464)

Having the test in the header requires including unistd.h on POSIX
platforms. This header has other declarations which may conflict with
code that uses named declarations provided by this header. For example
code using "int pipe;" would conflict with the function pipe in this
header.

Moving the code to the dylib means std::print would not be available on
Apple backdeployment targets. On POSIX platforms there is no transcoding
required so a not Standard conforming implementation is still a useful
and the observable differences are minimal. This behaviour has been done
for print before https://github.com/llvm/llvm-project/pull/76293.

Note questions have been raised in LWG4044 "Confusing requirements for
std::print on POSIX platforms", whether or not the isatty check on POSIX
platforms is required. When this LWG issue is resolved the
backdeployment targets could become Standard compliant.

This patch is intended to be backported to the LLVM-18 branch.

Fixes: https://github.com/llvm/llvm-project/issues/79782

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[libc++] Guard the whole print.cpp file with _LIBCPP_WIN32API (#71122)

The print.cpp source file is only used when building on Windows. Avoid
including anything else but <__config> in the file in t

[libc++] Guard the whole print.cpp file with _LIBCPP_WIN32API (#71122)

The print.cpp source file is only used when building on Windows. Avoid
including anything else but <__config> in the file in the case where
there's nothing to compile here at all. As a drive-by change, use
_LIBCPP_WIN32API consistently instead of _WIN32.

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[libc++] Adds __throw_system_error overload.

This was mention in D150044 and D154995 that this would be useful.
This addresses the last review coment of D150044.

Reviewed By: #libc, ldionne

Differ

[libc++] Adds __throw_system_error overload.

This was mention in D150044 and D154995 that this would be useful.
This addresses the last review coment of D150044.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D156019

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[libc++][print] Adds FILE functions.

Drive-by fix to make sure the __retarget_buffer works correctly whan
using a hint of 1. This was discovered in one of the new tests.

Drive-by fixes __retarget_b

[libc++][print] Adds FILE functions.

Drive-by fix to make sure the __retarget_buffer works correctly whan
using a hint of 1. This was discovered in one of the new tests.

Drive-by fixes __retarget_buffer when initialized with size 1.

Implements parts of
- P2093R14 Formatted output
- P2539R4 Should the output of std::print to a terminal be
synchronized with the underlying stream?

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D150044

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