Pragma-like comment to suppress --warn-undefined-variables

[singalen]

--warn-undefined-variables is really useful, but some modules are relying on undefined variables being empty, and they generate the checks in thousands. Not always they can be rewritten.
In this cases, it would be beneficial to have a pragma-like comment to suppress the warning for some of lines.
grep-ing them out would only help if the code testing the variable is not in $(eval).

[rocky]

Ok. Want to try your hand at addressing this in a PR?

[singalen]

I might. No promises, though - I'm overcommitted for the nearest month.
Considering that grep works nearly as well...