PS> 3.5 loop2 = beta so anything can likely go wrong.
Might rather want to use say 3.4 mini or 3.4F or even PE1.1 + updates / fixes then compile FreeOrion.
See Wolfdens upgrade guide or
# emerge -e world
or portato can do it as well.
# revdep-rebuild -X
gentoolkit pulls this in I think.
PE1.1 = x86 = stable portage tree.
others = ~x86 unstable / testing portage tree and so can add below as well.
# emerge udept
# dep --help
3.5 loop* is all little green men walking on Planet Venus and driving Buicks or something = far out = cutting edge + possibly lots of unstable / bugs not yet found for what you need.
The users of FreeOrion would likely only get close to 3.4F in 8 months , so 3.5 loop* is 16 months to 32 months ahead of anything out there now that other linux users might dream off updating too in the future.
You can rather create and then port it to a later version of ?? once ready / stable and so stay with the crowd in linux + have least incompatibility.
Hope this helps.