Change the per-project option file to be `.gutctags` and process it first. When using Gutentags with a cache directory put all the tag files in, the `ctags` executable will be run against absolute paths, because the output paths in the tag file will also need to be absolute in order to make it possible to open them in an editor. This means exclude rules need to be run against absolute paths too, so we make those rules absolute and store the result in a temporary file that we pass to `ctags` as the real options file.