Register _cleanup function with atexit

* Register cleanup function with atexit
   instead of calling it explicitly on
   exit()
 * abort() no longer calls _cleanup:
   Flushing stdio buffers on abort is no
   longer required by POSIX.
 * dlmalloc no longer need to reset cleanup
   (see above)
 * Upstream findfp.c makebuf.c setvbuf.cexit.c
   to openbsd versions.

Bug: 14415367
Change-Id: I277058852485a9d3dbb13e5c232db5f9948d78ac

libc/bionic/abort.cpp

@@ -32,8 +32,6 @@
 #include <unistd.h>
 #include "atexit.h"
 
-__LIBC_HIDDEN__ void (*__cleanup)();
-
 #ifdef __arm__
 extern "C" __LIBC_HIDDEN__ void __libc_android_abort()
 #else
@@ -47,11 +45,6 @@ void abort()
   sigdelset(&mask, SIGABRT);
   sigprocmask(SIG_SETMASK, &mask, NULL);
 
-  // POSIX requires we flush stdio buffers on abort.
-  if (__cleanup) {
-    (*__cleanup)();
-  }
-
   raise(SIGABRT);
 
   // If SIGABRT ignored, or caught and the handler returns,