Add config for gccdiag?

[randrej]

I've written a tool that helps you get lint information from gcc, but with regards to the compile_commands.json. It's better than just calling gcc -o /dev/null because it gets the proper flags from the compilation database. This allows the compilation (which does linting alongside) to succeed almost always.

The tool can be found here. I have an efm-langserver config for it in the readme there, take a look.

Would you be interested in adding the config to the example config here? Thanks!