Given following log snippets, their explanation, and nothing else, explain what failure, if any, occurred during build of this package.

  Snippets are in a format of [X] : [Y], where [X] is a log snippet, and [Y] is the explanation.

  Snippets are delimited with '================'.

  Drawing on information from all snippets, provide a concise explanation of the issue and recommend a solution.

  Explanation of the issue, and recommended solution, should take a handful of sentences.

  Snippets:

  [../src/backlight/backlight.c: In function âread_brightnessâ:
../src/backlight/backlight.c:389:21: error: unused variable âsubsystemâ [-Werror=unused-variable]
  389 |         const char *subsystem, *value;
      |                     ^~~~~~~~~]: [Build failed during compilation of src/backlight/backlight.c

There is an unused variable `subsystem`]

Issue: Compiler detected unused variable
Resolution: Check if unused variables are needed or not. If yes, then use them; otherwise, remove them.