Installing packages on Gentoo is as easy as on any Linux platform.

Emerge gputils.

emerge -av gputils

For now, version 2.5 of SDCC is officialy supported so add the corresponding rule in one of your /etc/portage/packages.keywords files and emerge sdcc.

cat '=dev-embedded/sdcc-2.5*' >> /etc/portage/packages.keywords/mios
emerge -av sdcc