ch341a_spi is missing in IUSE (changed some weeks ago, but I noticed it two days ago) After adding it to the list of programmers all works OK.
thanks ... should be fixed here: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=1fd2864c6a0c7dbc206800d327826a447f6cf5d7
Fine! :-)