If you try to emable CONFIG_REISERFS_FS_XATTR_USER without CONFIG_REISERFS_FS_POSIX_ACL, compilation of the kernel will fail because xattr_user.c has some calls to reiserfs_permission_locked. Somf #ifdef CONFIG_REISERFS_FS_POSIX_ACL 's around the calls in user_get,user_set, and user_del will clear it up. I notice this problem in hardened-sources-2.4.24-r1, but it is likeley present elsewhere...
Can't even see this option in hardened-sources-2.4.26-r1 - are there other kernels where you have seen this issue?
Seeing as how 2.4.26 doesn't have this option any more... this bug can probably be closed.