Also neuter __isthreaded.
We should come back to try to hide struct FILE's internals for LP64.
Bug: 3453512
Bug: 3453550
Change-Id: I7e115329fb4579246a72fea367b9fc8cb6055d18
This is part of the upstream sync (Net/Open/Free BSDs expose the
nameser.h in their public headers).
Change-Id: Ib063d4e50586748cc70201a8296cd90d2e48bbcf