Add default configuration for Clang language server daemon (clangd)

[mustafakemalgilor]

Currently, `clangd' is enabled by default, but proper configuration for it is missing. This causes false error squiggles in vscode.

[mustafakemalgilor]

Apparently, clangd has compile_commands.json reading ability. It searches the json file in project root directory. Hadouken now creates a symlink from <project_root>:/build/compile_commands.json to <project_root>:/compile_commands.json. clangd now properly recognizes include files and compilation flags.

Since clangd doesn't understand some of the gcc specific arguments, it might be a good idea to disable clangd when selected kit is gcc though.