Created attachment 575554 [details] build.log This issue is present since the last commit to the git repository.
Created attachment 575556 [details] emerge --info sys-fs/go-mtpfs
same issue here.
Just in case someone wants to be able to build the package - you can use the EGIT_COMMIT variable to specify the latest functioning commit (currently c73e8c1410229fead1d57cfd28017637b86e5121) for me.
9999 is no longer in the tree