packages: Make create-sets.sh more robust

[ivy]

Summary

Use ${PKG_CMD} rather than bare 'pkg' to fix the build when pkg is
not in the tools path. Provide a default in case it's not set for
some reason (e.g., running the script by hand).

Since set -- $(...) does not trigger an exit from set -e if the
command fails, this failure was silent and resulted in sets not
being built correctly if we failed to run pkg. Use a temporary
variable, which does trigger set -e, to fail correctly.

MFC after: 2 weeks
Sponsored by: https://www.patreon.com/bsdivy

[sjg]

release/packages/create-sets.sh

29

the quotes are unnecessary fwiw

48–49

again fwiw the outer quotes are not required
is the switch to 2 steps just to aid debugging ? i don't see _tmp used elsewhere

[ivy]

release/packages/create-sets.sh

48–49

the reason is that this does not trigger set -e:

set -- $(nonesuch)

while this does:

_tmp=$(nonesuch)
set -- $_tmp

so we need this to fail properly if $(nonesuch) fails, which in this case it will if $PKG_CMD isn't found for some reason.

[sjg]

fair enough