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
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
