sys-devel/crossdev build the tool how can use ~ like ~amd

[vastchen]

I was saw this two links :
https://wiki.gentoo.org/wiki/Raspberry_Pi/Cross_building
and
https://wiki.gentoo.org/wiki/Overlay/Local_overlay
i have a raspberry 3 install gentoo and a old core2 cpu computer, this computer build the software is slow.
so i want the raspberry help computer build the software.

but in my computer use gcc5.4 but use the raspberry sys-devel/crossdev
crossdev -S -v -t x86_64-pc-linux-gnu
but build the gcc is stable 4.8 how can i use ~amd gcc4.5 in crossdev?
_________________
gentoo user

[vastchen]