gh-135755: Make Py_TAIL_CALL_INTERP macro private

[vstinner]

Rename Py_TAIL_CALL_INTERP to _Py_TAIL_CALL_INTERP.

• Issue: Undocumented 3.14 C API #135755

[vstinner]

@Fidget-Spinner: I blindly replaced Py_TAIL_CALL_INTERP text with _Py_TAIL_CALL_INTERP. I didn't test my change.

[Fidget-Spinner]

Thanks. I'll approve once CI passes.

[vstinner]

I built Python with tail call on Linux using ./configure --with-tail-call-interp CC=clang LD=clang && make. I checked that ./python -m test test_sys -v still pass.

[Fidget-Spinner]

I built Python with tail call on Linux using ./configure --with-tail-call-interp CC=clang LD=clang && make. I checked that ./python -m test test_sys -v still pass.

Don't worry, we have CI for the tail calling interpreter on most platforms, so you can just let it run :)

[vstinner]

Ping @Fidget-Spinner

[vstinner]

@hugovk: This change mostly/only makes sense if it's backported to 3.14. Would you accept this late C API change in 3.14? It makes the macro private.

[vstinner]

Maybe it's ok to leave the macro in 3.14 and remove it in 3.15. No one should rely on this macro :-)

[miss-islington-app]

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @vstinner, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 6504f20ccedf0b27275327e72698dee5f0c75ba8 3.14 

[bedevere-app]

GH-139120 is a backport of this pull request to the 3.14 branch.

[vstinner]

@Fidget-Spinner suggested me to merge this change in the main branch, so I did it :-)