Summary:
Use of `__attribute__` and `__unused` is compiler specific. Opt for standard `[[maybe_unused]]` instead.
## Changelog
[General] [Fixed] - Remove compiler-specific syntax.
Pull Request resolved: https://github.com/facebook/react-native/pull/34357
Test Plan: Built on react-native-windows.
Reviewed By: cipolleschi
Differential Revision: D38498481
Pulled By: javache
fbshipit-source-id: af43206788f54dda3b747b6417e20096c7d520e8