gh-128563: Move assignment of opcode into ifdef by Fidget-Spinner · Pull Request #129803 · python/cpython
This moves the opcode assignment into the tail call ifdef, to aid with really old compilers that might not be able to optimize it away.
Though we might think a single assignment doesn't matter. I have a feeling it's not optimized away.
See the comment thread from #128563 (comment) onwards for rationale.