I've created a patch that just changes the enum variable to enumer for broken classes. It's now compiling for me under Java 1.5 (sun-jdk-1.5.0.06), and concidering the minor change it would be safe to apply the patch globally.
Created attachment 77630 [details] commons-pool-1.2-r2.ebuild Added an epatch line.
Created attachment 77631 [details, diff] commons-pool-1.2-jdk1.5-enum.patch The mentioned patch, changes StackKeyedObjectPool.java and StackObjectPool.java.
*** This bug has been marked as a duplicate of 69970 ***