Feature request for --error-undefined-variables

[R. Diez]

Hi all:

Makefiles can become complex beasts, and option "--warn-undefined-variables" 
helps find programming errors.

Unfortunately, makefiles also tend to generate a lot of text, and therefore 
such warnings can be easily missed. This reduces the usefulness of 
"--warn-undefined-variables" to a great extent.

I would like to have a flag like "--error-undefined-variables" instead, which 
would be the equivalent to Bash' option "set -o nounset". This way, such 
programming errors cannot go undetected any more.

Best regards,
  rdiez