Improve <sys/cdefs.h>.

Fix and use __RENAME (and lose ___RENAME --- two underscores should be
enough for anybody). This was the point of this change, because I want
to use __RENAME to support the two basename variants and the two
strerror_r variants.

Lose a bunch of macros that weren't being used.

Lose three dead files from the DNS code.

Bug: 17784968

(cherry picked from commit 2cfb4e8e)

Change-Id: I5e96146f92c0521248c78c0933bec5e9a9818222