It seems the man page for binutils is outdated. The manpage of binutils-config-5-r2 states that the program accepts options '--gold' and '--bfd'. However, asking the executable it tells that it only understands '--linker <name>'. Also '--debug', '--version', '--help' are undocumented (the last two even in the --help message of the program). I don't know if there are any other parts of the man page which are outdated.
should be fixed with: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=dedaa68dc7a03197db17e9ff25f22bf7454afbc4 thanks for the heads up!