Fix a couple of make-temp-file races

Fix a couple of make-temp-file races

* lisp/emacs-lisp/autoload.el (autoload--save-buffer):
* lisp/emacs-lisp/bytecomp.el (byte-compile-file):
Use make-temp-file, not make-temp-name, to avoid an unlikely race
that could lose data.  Remove the deletion hook as quickly as
possible after the file is renamed; though a race still remains
here, it is smaller than before.