Compile with -Wsign-compare flag

[mergennachin]

🚀 The feature, motivation and pitch

Follow up to #8016

For gcc9, it is failing with sign-compare errors (https://gist.github.com/mergennachin/af7abbdaf24ac5c63ee40284c04aee61)

For now, I disabled that but we should make sure to clean those errors

Alternatives

No response

Additional context

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RFC (Optional)

No response

cc @JacobSzwejbka @dbort

[mergennachin]

Addressed by #8581