Consider making %buildsystem_name_conf optional

[hroncok]

%conf is an optional section. Hence, I believe mandating the presence of %buildsystem_name_conf for a declarative buildsystem is suboptimal.

I was able to "solve" this by:

%buildsystem_name_conf() %nil

However, that seems rather boilerplate-like.

Is there a reason to force the presence of %buildsystem_name_conf?

[pmatilai]

Opened #3244 from this, along with a more elaborate answer why it's that way. Thanks for the suggestion.