Consider labels of inline asm as conditionally executed

[samueltardieu]

Since an asm!() statement is mostly unknown, as we do not know what it does, consider all labels' break as being conditionally executed only.

Fixes #15673

changelog: [never_loop]: do not consider break labels used in asm!() as being unconditionally executed as they might not be

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This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

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