The poisoned_hash_helper header was relying on an implicit forward
declaration of std::hash located in <type_traits>. When we improve the
modularization of the library, that causes issues, in addition to being
a fundamentally non-portable assumption in the test suite.

It turns out that the reason for relying on a forward declaration is to
be able to test that std::hash is *not* provided if we don't include any
header that provides it. But testing that is actually both non-portable
and not really useful.

Indeed, what harm does it make if additional headers provide std::hash
specializations? That would certainly be conforming -- the Standard
never requires an implementation to avoid providing a declaration when a
given header is included, instead it mandates what *must* be provided
for sure. In that spirit, it would be conforming for e.g. `<cstddef>` to
define the hash specializations if that was our desire. I also don't
read https://wg21.link/P0513R0 as going against that statement. Hence,
this patch just removes that test which doesn't carry its weight.

Fixes #56938

This applies clang-format to the std::string unit tests in preparation
for landing https://reviews.llvm.org/D140550.

Differential Revision: https://reviews.llvm.org/D140612

This has been done using the following command

  find libcxx/test -type f -exec perl -pi -e 's|^([^/]+?)((?<!::)size_t)|\1std::\2|' \{} \;

And manually removed some false positives in std/depr/depr.c.headers.

The `std` module doesn't export `::size_t`, this is a preparation for that module.

Reviewed By: ldionne, #libc, EricWF, philnik

Differential Revision: https://reviews.llvm.org/D146088

This is in response to failures seen after landing D138307.

Differential Revision: https://reviews.llvm.org/D138596

Also implement LWG3705.
Fixes https://github.com/llvm/llvm-project/issues/55823

Reviewed By: ldionne, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D132338

Many tests in `libcxx/test/std/strings` use
`#if defined(__cpp_lib_char8_t) && __cpp_lib_char8_t >= 201811L`
which can be replaced with the more terse `#ifndef TEST_HAS_NO_CHAR8_T`.

Differential Revision: https://reviews.llvm.org/D132626

It's not tested or used anymore -- instead a Clang-based compiler is
used on IBM nowadays.

Differential Revision: https://reviews.llvm.org/D127650

This avoids using an libc++ internal macro in our tests.

Reviewed By: #libc, philnik, ldionne

Differential Revision: https://reviews.llvm.org/D118832

Some embedded platforms do not wish to support the C library functionality
for handling wchar_t because they have no use for it. It makes sense for
libc++ to work properly on those platforms, so this commit adds a carve-out
of functionality for wchar_t.

Unfortunately, unlike some other carve-outs (e.g. random device), this
patch touches several parts of the library. However, despite the wide
impact of this patch, I still think it is important to support this
configuration since it makes it much simpler to port libc++ to some
embedded platforms.

Differential Revision: https://reviews.llvm.org/D111265

C++98 and C++03 are effectively aliases as far as Clang is concerned.
As such, allowing both std=c++98 and std=c++03 as Lit parameters is
just slightly confusing, but provides no value. It's similar to allowing
both std=c++17 and std=c++1z, which we don't do.

This was discovered because we had an internal bot that ran the test
suite under both c++98 AND c++03 -- one of which is redundant.

Differential Revision: https://reviews.llvm.org/D80926