We had these symbols incorrectly versioned as LIBC_PRIVATE
in M release. This change moves __aeabi* symbols from LIBC
to LIBC_N and adds __gnu_Unwind_Find_exidx to the list
Bug: https://github.com/android-ndk/ndk/issues/1
Change-Id: I0b353012adeacb00ae29ea10c63b9d1cf1cadbe7