Make: minor changes

[masatake]

• extract macros assigned with != operator
• skip override directive

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 85.42%. Comparing base (7cc5308) to head (37a7477).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #4028 +/- ## ======================================= Coverage 85.42% 85.42% ======================================= Files 235 235 Lines 56728 56729 +1 ======================================= + Hits 48461 48462 +1 Misses 8267 8267 ```

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