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 194847 [details]
This was a random fix made by me...no real interest to fix it...maybe when the time for Glibc 2.10 stabilisation has come.
Created attachment 197393 [details, diff]
fix name clash for svgalib internal round function
I just ran across this myself and the attached patch fixes the
problem assuming I understand the intentions of the svgalib
*** Bug 270316 has been marked as a duplicate of this bug. ***
Fixed in portage, thanks to Markus for the patch.