Unversion some symbols for the NDK.

These functions were erroneously released in LIBC_PRIVATE for M, but
in fact need to be public. Since we need to be able to load them on M
even if they were built for a lower platform (and M needs to load on
newer platforms), we need to unversion them.

Change-Id: I333fe8ae7380cc2a5dbd699414399ec52f602383