Prepare CXX_MODULE usage

[ClausKlein]

This is a prototype only to evaluate some concepts how we can work with CXX_MODULES

see too cmake/README.md

Create a self contained CXX_MODULE

Add module usage example.

All examples will be tested in Release build within a find-package-test using staged install to build directory

BEMAN_USE_STD_MODULE=OFF only for llvm

• Local fix only to install modules right!
• some historic compiler should not longer used / supported (i.e.: gcc-14, clang-18, clang-19)!
• for all current clang compiler on Linux, cmake -D BEMAN_USE_STD_MODULE=OFF should be used on CI!
• install test on CI should not longer needed or must be changed to Ninja instead default generator?
• Cookiecutter is a nightmare, Not yet started! The concept has to be approved and the infra PR merged!

It depends on following PR:

• Update CMake and Ninja versions when running MSVC/AppleClang builds infra-workflows#19
• Install FILE_SET CXX_MODULES too infra#13
• Feature/add cxx modules rules infra#16
• Feature/add prelude.cmake module infra#17

fix #287 too
and some aspects of #59

[coveralls]

coverage: 100.0%. remained the same
when pulling deac326 on ClausKlein:feature/add_cxx_module
into ddfe5ba on bemanproject:main.

[ClausKlein]

@ednolan Please help, I can't fix some of the CI problems caused by infra structure

I disabled on CI C++26 tests with historic appleclang, gcc-13, clang-17, clang-18

[ClausKlein]

@ednolan I disable the gcc-13 tests on CI for now

see ticket #290

and C++26 is not usable with apple clang, see #289

eb59178

[ClausKlein]

the full log of:

bash-5.3$ make -n demo
rm -rf build stagedir compile_commands.json
find . -name '*~' -delete
rm -rf /opt/local/*/*
cmake --preset appleclang-release --fresh --log-level=VERBOSE
cmake --workflow appleclang-release
cmake --preset gcc-release --fresh --log-level=VERBOSE
cmake --workflow gcc-release
cmake --preset llvm-release --fresh --log-level=VERBOSE
cmake --workflow llvm-release
cmake --preset llvm-debug --fresh --log-level=VERBOSE
cmake --workflow llvm-debug
cmake --install build/llvm-debug --prefix=/opt/local
cmake --install build/llvm-release --prefix=/opt/local
tree /opt/local

bash-5.3$ tree /opt/local
/opt/local
├── bin
├── etc
├── include
│   └── beman
│       └── exemplar
│           └── identity.hpp
├── lib
│   ├── cmake
│   │   └── beman.exemplar
│   │       ├── beman.exemplar-config-version.cmake
│   │       ├── beman.exemplar-config.cmake
│   │       ├── beman.exemplar-targets-debug.cmake
│   │       ├── beman.exemplar-targets-relwithdebinfo.cmake
│   │       ├── beman.exemplar-targets.cmake
│   │       ├── cxx-modules
│   │       │   ├── cxx-modules-beman.exemplar-targets-Debug.cmake
│   │       │   ├── cxx-modules-beman.exemplar-targets-RelWithDebInfo.cmake
│   │       │   ├── cxx-modules-beman.exemplar-targets.cmake
│   │       │   ├── target-exemplar-Debug.cmake
│   │       │   └── target-exemplar-RelWithDebInfo.cmake
│   │       └── modules
│   │           └── identity.cppm
│   ├── libbeman.exemplar.a
│   └── libbeman.exemplar_d.a
└── share

12 directories, 14 files

build-cz7u1udb.log

[ClausKlein]

This was only created to demonstrate one possible concept and to end in a discussion how to use CXX_MODULES in a Beman project.

The discussion should continue https://discourse.bemanproject.org/t/c-20-modules-in-beman-project-libraries/279/39?u=clausklein here