A test case for correct handling of temporary directory deletion that
was added to check.sh as part of PR #2689 was initially disabled for
Darwin because of a directory permission issue in PR #2688.
Now that the issue in PR #2688 is fixed, this commit enables the test
case for Darwin.
With --check and the --keep-failed (-K) flag, the temporary directory
was being retained regardless of whether the build was successful and
reproducible. This removes the temporary directory, as expected, on
a reproducible check build.
Added tests to verify that temporary build directories are not
retained unnecessarily, particularly when using --check with
--keep-failed.
