The interpreter generator has long supported giving it multiple bytecodes files where the latter files override opcodes defined in the earlier opcodes. This enables PEP 523 hook users to generate an interpreter loop using the existing opcodes and their own set of customizations. But there've been no test cases that validate this actually works.

This adds such a test case and fixes things up so this practically works. static functions used directly in the interpreter loop are moved into ceval.h. APIs which are used but not exported are marked as exported.

Linked PRs

• gh-142913: Add test case for interpreter generator w/ overridden opcodes #142911