build: create compile_commands.json on build

[demo-exe]

adding compile_commands.json to gitignore and creating it with cmake enables editors to use LSP.
You can now symlink it to build dir or copy/modify it in repo root.

[mgumz]

what does it do?

[demo-exe]

it allows clangd lsp to work - compile_commands is a list of clang calls basically.
compile_commands in root is ln -s to actual in build-root

[mgumz]

@demo-exe put this into the commit message.

[mogaika]

Isn't such compile_commands.json will contain global paths like -I/src/build-root -I/src/build-root/vpp_plugins/upf?

[demo-exe]

Depends on where you run cmake.
Anyway, the internet seems to have no better option for developing inside docker containers than to install editor inside it.

[demo-exe]

after some discussion, added the file to gitignore, this allows for more diverse setups like semi-local builds

[mgumz]

@demo-exe "fix" … fix what? Can you merge your "fix" into the appropriate commit

[demo-exe]

do not worry, in our flow everything gets squashed at merge :)