update compile_commands generation to be compatible with C++20 modules (bug?)

[metasprite]

Is your feature request related to a problem? Please describe.

The compile_commands.json generated by xmake doesn't help language servers like clangd find C++20 module files. My project with C++20 modules compiles fine, but clangd can't find imported modules, so it complains.

Describe the solution you'd like

Extend compile_commands.json generation to tell the compiler where modules can be found.
For clang on linux, adding -fprebuilt-module-path=build/.gens/test/linux/x86_64/release/rules/modules/cache to the compile_commands.json generated by xmake works. clangd behaves as expected after doing this.

I see how this is implemented in build_modules/clang.lua:

target:add("cxxflags", "-fimplicit-modules", "-fimplicit-module-maps", "-fprebuilt-module-path=" .. cachedir, {force = true})

I'm just not sure how to make the compile_commands.json generation code use this...

Describe alternatives you've considered

I wasn't sure whether this was a bug report or feature request, so I don't see another way to fix this problem.

[waruqi]

not supported yet, see #1167

[waruqi]

we have supported it, you can try cxxmodules branch. #2641

However, vscode and other editor/ide should not yet support complie_commands with c++modules.

[waruqi]

but vscode and other some ide maybe still not support compile_commands.json with c++modules.

microsoft/vscode-cpptools#6302 (comment)

[waruqi]

I have merged it now.