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 194661 [details]
fardata.c: In function 'error_proc':
fardata.c:48: warning: unused variable 'tmp_errmsg'
fardata.c:61: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result
fardata.c: At top level:
fardata.c:193: error: conflicting types for 'strnlen'
/usr/include/string.h:404: note: previous declaration of 'strnlen' was here
28 Jun 2009; Patrick Lauer <email@example.com> arj-3.10.22-r2.ebuild,
Fix for glibc 2.10 compilation. Patch by hirakendu. Solves #271608
*** This bug has been marked as a duplicate of bug 271608 ***