Improve C++20 modules support

[waruqi]

• improve parallel compilation
• support headerunits (stl & user)
• improve scan moduledeps
  • msvc (/scanDependencies + fallback)
  • clang (fallback)
  • gcc (-fdep-format=trtbd + fallback)
• project generator
  • support cmakelists
    • gcc
    • clang
    • msvc
  • support vs (we need support add flags for sourcefiles)
  • support compile_commands
  • improve and reduce cmakelists

related pr

• [Draft] Improve C++20 modules support #2623
• Improve MSVC and clang modules compilation #2664
• improve generator for cxxmodules #2673

related issues

• update compile_commands generation to be compatible with C++20 modules (bug?) #2114
• [C++20 Modules] Support of automatic header-unit compilation #1953
• Optimal parallelization of targets for C++20 modules #1862
• clang c++20 modules missing information in compile_commands.json exported #1167
• Improve generated cmakelists #2410
• Optimal parallelization of targets for C++20 modules #1862
• Add IntelliSense for C++20 modules importing microsoft/vscode-cpptools#6302 (comment)

[waruqi]

@Arthapz I have improved some codes. e.g. toolchain includedirs, fix bmi flags for msvc, format code and optimize performance...

I still need to understand the code in depth, maybe it will take some time.

[waruqi]

mmmmh, when building a shared lib with header units, we may have link error because the library consummer don't have access to the header units .obj, i think i need some more reading about header units to handle that we may handle them wrong

well, you can add a shared test example in tests directory first.

[waruqi]

cmake generator work fine for gcc/clang now.

$ xmake project -k cmake; cd build/; cmake ..; make 
[  0%]: generating.cxx.module.deps src/hello_impl.cpp
[  0%]: generating.cxx.module.deps src/main.cpp
[  0%]: generating.cxx.module.deps src/mod_impl.cpp
[  0%]: generating.cxx.module.deps src/hello.mpp
[  0%]: generating.cxx.module.deps src/mod.mpp
create ok!
-- The CXX compiler identification is GNU 11.3.0
-- The C compiler identification is GNU 11.3.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /mnt/xmake/tests/projects/c++/modules/dependence/build
[ 20%] Generating output_dependence_ADE56AE0
[ 0%]: generating.cxx.module.bmi mod
[ 0%]: generating.cxx.module.bmi hello
[ 20%] Built target target_dependence_ADE56AE0
[ 40%] Building CXX object CMakeFiles/dependence.dir/src/hello_impl.cpp.o
[ 60%] Building CXX object CMakeFiles/dependence.dir/src/main.cpp.o
[ 80%] Building CXX object CMakeFiles/dependence.dir/src/mod_impl.cpp.o
[100%] Linking CXX executable linux/x86_64/release/dependence
[100%] Built target dependence

[waruqi]

The vs generator is not currently supported because it requires all cxxflags to be fetched in advance of the config phase, but some of the module's cxxflags are dynamically added in before_build_files, so they cannot be fetched.

This patch is a bit large and works mostly fine for now, so I've merged it for now, other improvements to vs generator and shared libs can be improved in a new patch separately.