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 2cfb4e8e2e217ef0e4140dcbf9b3da809781158c)

Change-Id: I5e96146f92c0521248c78c0933bec5e9a9818222
diff --git a/libc/include/fcntl.h b/libc/include/fcntl.h
index 8f89afb..87c8481 100644
--- a/libc/include/fcntl.h
+++ b/libc/include/fcntl.h
@@ -84,9 +84,9 @@
 #if defined(__BIONIC_FORTIFY)
 
 extern int __open_2(const char*, int);
-extern int __open_real(const char*, int, ...) __asm__(__USER_LABEL_PREFIX__ "open");
+extern int __open_real(const char*, int, ...) __RENAME(open);
 extern int __openat_2(int, const char*, int);
-extern int __openat_real(int, const char*, int, ...) __asm__(__USER_LABEL_PREFIX__ "openat");
+extern int __openat_real(int, const char*, int, ...) __RENAME(openat);
 __errordecl(__creat_missing_mode, "called with O_CREAT, but missing mode");
 __errordecl(__creat_too_many_args, "too many arguments");