make check: Eliminate "operation not permitted" errors

[patmaddox]

aftercheck calls clean. ${DESTDIR}/var/empty has schg flag set. Prior to this change, every run of make check ended with:

rm: checkdir/var/empty: Operation not permitted
rm: checkdir/var: Directory not empty
rm: checkdir: Directory not empty
*** Error code 1 (ignored)

Remove the flags from DESTDIR before running clean, to bypass the noisy output.

[patmaddox]

Original code:

# NOTE: this is intentional to ensure that "make check" can be run multiple
#       times. "aftercheck" won't be run if "make check" fails, is interrupted,
#       etc.
aftercheck:
	@cd ${.CURDIR} && ${MAKE} clean
	@test ! -e ${DESTDIR} || chflags -R 0 "${DESTDIR}"
	@rm -Rf "${DESTDIR}"

It's not clear to me if the "this is intentional" comment means that it's intended to set flags after clean, and letting these errors through. That seems strange to me. edit: I think it means that it's intended to put this logic in aftercheck rather than in check, for the "fails, is interrupted, etc" reason.

I addressed this because when running the tests, it was unclear to me if something was wrong with my setup. Error messages shouldn't come up as a part of a normal test run, unless they're expected.

Also: I don't know if this is the sort of thing I should make a Problem Report first for? So a Bugzilla PR "make check gives noisy operation not permitted errors" so there's a place to track / discuss it, and then a github PR to fix it?

Seemed small enough to me that I could just make a GH PR.

---

Also, is there any reason this shouldn't be part of make clean itself?

[brooksdavis]

The commit message in 38f8fdd has some backstory. I've added @ngie-eign as a reviewer.