[libc++] Reland CI module improvements.

Revert "Revert #76246 and #76083"

This reverts commit 5c150e7eeba9db13cc65b329b3c3537b613ae61d.

Adds a small fix that should properly disable the tests on W

[libc++] Reland CI module improvements.

Revert "Revert #76246 and #76083"

This reverts commit 5c150e7eeba9db13cc65b329b3c3537b613ae61d.

Adds a small fix that should properly disable the tests on Windows.
Unfortunately the original poster has not provided feedback and the
original patch did not fail in the LLVM CI infrastructure.

Modules are known to fail on Windows due to non compliance of the
C library. Currently not having this patch prevents testing on other
platforms.

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Revert #76246 and #76083

These cause test build failures on Windows.

This reverts the following commits:
57ca74843586c9a93c425036c5538aae0a2cfa60
d06ae33ec32122bb526fb35025c1f0cf979f1090

[libc++][modules] Adds module testing. (#76246)

This adds a new module test infrastructure. This requires tagging tests
using modules. The test runner uses this information to determine the
compi

[libc++][modules] Adds module testing. (#76246)

This adds a new module test infrastructure. This requires tagging tests
using modules. The test runner uses this information to determine the
compiler flags needed to build and use the module.

Currently modules are build per test, which allows testing them for
tests with ADDITIONAL_COMPILE_FLAGS. At the moment only 4 tests use
modules. Therefore the performance penalty is not measurable. If in the
future more tests use modules it would be good to measure the overhead
and determine whether it's acceptable.

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[libc++][modules] Removes module testing. (#76083)

This removes the entire modules testing infrastructure.

The current infrastructure uses CMake to generate the std and std.compat
module. This r

[libc++][modules] Removes module testing. (#76083)

This removes the entire modules testing infrastructure.

The current infrastructure uses CMake to generate the std and std.compat
module. This requires quite a bit of plumbing and uses CMake. Since
CMake introduced module support in CMake 3.26, modules have a higher
CMake requirement than the rest of the LLVM project. (The LLVM project
requires 3.20.) The main motivation for this approach was how libc++
generated its modules. Every header had its own module partition. This
was changed to improve performance and now only two modules remain. The
code to build these can be manually crafted.

A followup patch will reenable testing modules, using a different
approach.

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[libc++] Renames modules-build.

This is a followup of D157625. Using the name clang-modules-build makes
it clear this is regarding the clang modules and not the C++23 std or
std.compat module.

Revi

[libc++] Renames modules-build.

This is a followup of D157625. Using the name clang-modules-build makes
it clear this is regarding the clang modules and not the C++23 std or
std.compat module.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D158927

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[libc++][CI] Test std module in C++26 mode.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D153408

[libc++][modules] Simplifies C++20 module testing.

The building of the std module has been moved from `params.py` and
`dsl.py` to a `lit.local.cfg` for the entire test suite. In theory this
change a

[libc++][modules] Simplifies C++20 module testing.

The building of the std module has been moved from `params.py` and
`dsl.py` to a `lit.local.cfg` for the entire test suite. In theory this
change allows testing modules in most configurations, except:
- combined with clang modules
- C++ versions that don't support the std module

Currently only C++23 with all parts enabled works.
C++26 is expected to work properly with CMake 3.27. That versions of CMake
knows how to invoke clang using C++26.
The parts disabled modi of libc++ have not been modularized yet.

It still is the goal that in the future CMake will be able to do the work
done in `lit.local.cfg`. Doing this in CMake would require a more mature
libc++ implementation.

Thanks a lot to @ldionne for giving hints how to enable modules in a
`lit.local.cfg`.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D157625

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[libc++][test] Fixes a typo in UNSUPPORTED.

[libc++][test] Fixes using modules in the test suite.

Importing modules in the test suite failed due to linker errors. This
fixes the issue and adds a minimal test to validate importing the std
modu

[libc++][test] Fixes using modules in the test suite.

Importing modules in the test suite failed due to linker errors. This
fixes the issue and adds a minimal test to validate importing the std
module works.

Reviewed By: #libc, philnik

Differential Revision: https://reviews.llvm.org/D156550

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