gh-101100: Fix Sphinx warnings in c-api/float.rst

[hugovk]

Fix these warnings by documenting the constant:

Doc/c-api/float.rst:109: WARNING: c:macro reference target not found: PY_BIG_ENDIAN
Doc/c-api/float.rst:140: WARNING: c:macro reference target not found: PY_BIG_ENDIAN

• Issue: Fix all Sphinx reference warnings in the documentation #101100

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📚 Documentation preview 📚: https://cpython-previews--113494.org.readthedocs.build/

[serhiy-storchaka]

If you document PY_BIG_ENDIAN, you should also document PY_LITTLE_ENDIAN.

And I think that float.rst is a wrong place for this. They have little relation to floats. Actually, the endianess of floating point representation can be different from the endianess of integer representation (see DOUBLE_IS_BIG_ENDIAN_IEEE754, DOUBLE_IS_LITTLE_ENDIAN_IEEE754 and DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754).

[hugovk]

Good point, these constants are defined in pyport.h, nothing to do with floats.

What do you recommend?

• Document the constants elsewhere - where?
• Silence these warnings with !
• Keep the warnings

[serhiy-storchaka]

I do not know what is the best place for them, this is why they are still not documented. I suggest to leave this as is, until we found good place (many other macros are not documented).

[hugovk]

Fine by me, let's tackle these later. Thanks for the review!