gh-131842: Allow to pass custom CFLAGS and LDFLAGS to the compilation of builtin extension modules

[pablogsal]

• Issue: Allow to pass custom CFLAGS and LDFLAGS to the compilation of builtin extension modules #131842

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📚 Documentation preview 📚: https://cpython-previews--131847.org.readthedocs.build/

[pablogsal]

Does someone has a better name for this flags? I don't like that we have PY_STDMODULE_CFLAGS and PY_STDMODULE_CFLAGS

[pablogsal]

I live in the past. I need to move all of this to 3.14 🤦

[vstinner]

You should add "needs backport to 3.13" label if you want to add this feature to Python 3.13.

[ned-deily]

A terminology question: builtin (or built-in) is used elsewhere to mean linked statically with the interpreter / python library, like here. The intent for this PR is to apply to all standard library extension modules, static and dynamically loaded, right? If so, we should find another word for the variables and descriptions.

[pablogsal]

A terminology question: builtin (or built-in) is used elsewhere to mean linked statically with the interpreter / python library, like here. The intent for this PR is to apply to all standard library extension modules, static and dynamically loaded, right? If so, we should find another word for the variables and descriptions.

Agreed. See #131847 (comment)

Any ideas of a better name?

[vstinner]

Any ideas of a better name?

I suggest to reuse the "extra" term: PY_EXTRA_STDMODULE_CFLAGS and PY_EXTRA_STDMODULE_LDFLAGS.

[ned-deily]

I think this PR warrants more discussion. See my comment on the issue.

[pablogsal]

Ok I answered in the issue let's move the discussion there #131842 (comment)

[python-cla-bot]

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[erlend-aasland]

Currently, we use PY_STDMODULE_CFLAGS for shared extension modules and PY_BUILTIN_MODULE_CFLAGS for built-in extension modules. This PR is slightly confusing, since it adds extra {C,LD}FLAGS for built-in extension modules using naming similar to what we use for shared extension modules.

I think we should follow the existing naming scheme, and I also think we should consider introduce variables for both shared and built-in modules. Alternatively, we could use a more neutral name (for example PY_EXTRA_MODULE_*FLAGS) and apply those to both shared and built-in extension modules.

[erlend-aasland]

Suggested change

	Equivalent flag to :envvar:`LDLAGS_NODIST` but it only applies to **all** builtin extension
	Equivalent flag to :envvar:`LDFLAGS_NODIST` but it only applies to **all** builtin extension

[erlend-aasland]

Suggested change

	* Two new configure flags are added: :envvar:`CFLAGS_BUILTIN_MODULE` and
	* Two new configure flags are added: :envvar:`PY_EXTRA_STDMODULE_CFLAGS` and

[erlend-aasland]

Suggested change

	:envvar:`LDFLAGS_BUILTIN_MODULE`. These flags allows refistributors to
	:envvar:`PY_EXTRA_STDMODULE_LDFLAGS`. These flags allows refistributors to