kern.post.mk: fix PORTSDIR handling

[yuri_aetern.org]

Summary

Using subshell's PORTSDIR variable (via $${PORTSDIR}}) seems to be
only working if PORTSDIR is specified directly on the make command
line.

Use ${PORTDIR} here instead so that setting the variable in
/etc/{make,src,src-env}.conf would work (also works for variable
being set on command line or in the environment).

Test Plan

Set PORTS_MODULES in /etc/make.conf and PORTSDIR in one of /etc/{make,src,src-env.conf}.

[imp]

I think this is right...
Also consider this approval by a source committer if you want to commit it :)

[jon_xyinn.org]

Just got a notice on my original bug report for this. Thanks for taking this on @yuri_aetern.org.

Minor question, what does the U stand for in ${PORTSDIR:U/usr/ports, I'm familiar with the other parts of shell variable substitution / replacement, but I haven't seen the U before haha.

[yuri_aetern.org]

In D37868#894488, @jon_xyinn.org wrote:

Just got a notice on my original bug report for this. Thanks for taking this on @yuri_aetern.org.

Minor question, what does the U stand for in ${PORTSDIR:U/usr/ports, I'm familiar with the other parts of shell variable substitution / replacement, but I haven't seen the U before haha.

It's a make(1) construct now, meaning the same as '-' in shell var subst.

[jon_xyinn.org]

In D37868#894489, @yuri_aetern.org wrote:

In D37868#894488, @jon_xyinn.org wrote:

Just got a notice on my original bug report for this. Thanks for taking this on @yuri_aetern.org.

Minor question, what does the U stand for in ${PORTSDIR:U/usr/ports, I'm familiar with the other parts of shell variable substitution / replacement, but I haven't seen the U before haha.

It's a make(1) construct now, meaning the same as '-' in shell var subst.

Thanks for that Yuri. I'll read up on that soon. Other than that, it seems good from what I see in the PR. I haven't tested yet but I don't have any concerns.