Add an 'ignore' node in the config to prevent compiling certain files/dirs

[maelanleborgne]

This is a tricky one.
SWC has an '--ignore' option, but it allows only a single path to be excluded (or at least I didn't manage to make it take multiple paths.)
So the solution I found was to pass a config snippet with --config-json (not documented on there website) to override the "exclude" config from .swcrc. This works, but SWC prints an error and exits with a 1 return code, so I had to disable printing the output of the command (which didn't print anything anyway) and apply a test on the error message to check if it's a 'real' error or just a notification that a file has been skipped.

Right now I think it's a very dirty hack, and I don't see any other solution but to ask on the swc repo to be able to bypass this.

If you'd like to give it a try go ahead 😃