pkglint: support${CC} inside sed string

[ng0 <ng0%n0.is@localhost>]

Hi,

for wip/nsm I have a not so odd workaround until
https://github.com/nifty-site-manager/nsm/pull/1/files
is merged.
The SUBST_SED does:
...
SUBST_SED.cc+=          -e 's,g++,${CXX:Q},g'
...

pkglint -Wall .  throws this warning:

WARN: Makefile:23: Please move ${CXX:Q} outside of any quoting characters.
1 warning found.
(Run "pkglint -e" to show explanations.)

however it just works as it should. If it's not too difficult,
can we add an exception for a situation like this to pkglint?