Clean up abort.

* A dlmalloc usage error shouldn't call abort(3) because we want to
  cause a SIGSEGV by writing the address dlmalloc didn't like to an
  address the kernel won't like, so that debuggerd will dump the
  memory around the address that upset dlmalloc.

* Switch to the simpler FreeBSD/NetBSD style of registering stdio
  cleanup. Hopefully this will let us simplify more of the stdio
  implementation.

* Clear the stdio cleanup handler before we abort because of a dlmalloc
  corruption error. This fixes the reported bug, where we'd hang inside
  dlmalloc because the stdio cleanup reentered dlmalloc.

Bug: 9301265
Change-Id: Ief31b389455d6876e5a68f0f5429567d37277dbc

libc/stdio/makebuf.c

@@ -65,7 +65,6 @@ __smakebuf(FILE *fp)
 		fp->_bf._size = 1;
 		return;
 	}
-	__atexit_register_cleanup(_cleanup);
 	flags |= __SMBF;
 	fp->_bf._base = fp->_p = p;
 	fp->_bf._size = size;