Do not leave files behind in /tmp from testing.

I noticed that glibc testsuite runs left several files behind in /tmp
(or TMPDIR, if different).  The problem was testcases that generate a
template for mkstemp / mkstemp64, ending with XXXXXX, then pass that
template to add_temp_file before calling mkstemp / mkstemp64, meaning
that the template ending with XXXXXX is stored in the list of
temporary files to delete (add_temp_file uses strdup so that the
original string doesn't need to stay live), not the actual filename as
determined by mkstemp / mkstemp64.  This patch fixes those tests to
call add_temp_file later.

Tested for x86_64 (that the files are no longer left behind by a
testsuite run and the modified tests still pass).

	* io/test-lfs.c (do_prepare): Do not call add_temp_file until
	after mkstemp64.
	* login/tst-utmp.c (do_prepare): Likewise.
	* rt/tst-aio.c (do_prepare): Likewise.
	* rt/tst-aio64.c (do_prepare): Likewise.