tests: fix false positive in failed test check for cmdline_wrap.at.

* tests/cmdline_wrap.at (fail_list): non-matching globs return as
a plain unexpanded string, so we also need to test for file
existence before expanding into fail_list.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
tests: update fat binary test case for modern darwin.

* tests/darwin.at: Use "-arch x86_64", which works on modern
Apple hardware, rather than "-arch ppc", which generally does not.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>