Fill the page size array in one posix shm test

[andrew]

Summary

The largepage_config posix shared memory test was failing on arm64 as
the page size array is never filled out. Fix this by calling
getpagesizes(3).

While here skip the test if there is no support for superpages.

[markj]

tests/sys/posixshm/posixshm_test.c

1258

pagesizes() already checks this.

[markj]

tests/sys/posixshm/posixshm_test.c

1258

I suspect it should just be (void)pagesizes(ps), to avoid reintroducing the warning that was fixed by cd16a848d1b34016b1a1c663223729a92c247be3.

[andrew]

Remove the page size check

[andrew]

tests/sys/posixshm/posixshm_test.c

1258

I agree, I'd already changed to that before seeing your second comment.