We have much better control over visibility now, so we don't need to
pollute the headers with cruft.
Bug: http://b/24767418
Change-Id: I349f4c3bc30102477375ad9f80926e560c7c1d8b
Not a public header file except in NetBSD, where it came from. Even
OpenBSD doesn't have it.
Bug: http://b/28519060
Change-Id: Id5feec4a4e8010a9f4433e73b1bfa6f935d884b9