These USE flags are not used in any gcc ebuilds since 3.4.6-r2, thus they should be removed.
i'm guessing you didnt read toolchain.eclass. n32/n64 are still in use. as for the other two, if Kumba doesnt know of any random location, they do seem to be dead now
the two ip* flags have been moved to gcc-3.4.6-r2