Check for unused variables in GN.

A check for unused variables was missing for some helper functions.
The main thing that this affects is the "config" function, where
people were confused when setting deps or configs didn't work the
way they expected (because they were unused).

BUG=392026
R=dpranke@chromium.org

Review URL: https://codereview.chromium.org/399143006

Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: a425c0d7d5acb3f1a47eef0639e436ff60522ba5
1 file changed