MFC r288444,r296586,r301753,r303840,r304175:

r288444 (by andrew):

Pass 8 arguments to makecontext on arm64 as this is all we support.

Obtained from: EuroBSDCon Devsummit

r296586 (by bdrewery):

Fix and connect setjmp test.

r301753:

Fix up r274061

Detect /usr/share/dict/words the "right way" by using require.files instead of
the hacked up attempt in the dict(..) function, which didn't work properly on
systems where MK_DICT == no.

r303840 (by jhb):

Add timer_settime tests using SIGEV_THREAD.

Note that these tests should work fine on NetBSD and other systems as
SIGEV_THREAD is POSIX.

r304175 (by ed):

Disable tests for non-standard behaviour of dirname(3)/basename(3).

The NetBSD ATF tests explicitly check that these functions do not modify
their input. These tests are NetBSD-specific. They test for something
that is not part of POSIX.

PR: 211873