There are a few changes in glibc-2.10 that might make your software fail to build with it, please refer to my blog post  if you're not sure what the problem is.
And no I don't usually provide emerge --info with these bugs because they are caused by glibc-2.10!
Created attachment 194125 [details]
Somebody dropped a patch…
Created attachment 211189 [details]
put it back, should work now.