Dealing with circular BuildRequires?

[Tom Lane]

So I started experimenting with updating libpng to a new release series,
and soon found out that it was impossible to rebuild its dependencies.
For example, cairo BuildRequires: librsvg2-devel, and librsvg2
BuildRequires: cairo-devel, so there is no order in which I can rebuild
them.  How the heck did we get into such a situation, and what should
I do about it?  Neither specfile appears to have any provision for
bootstrapping.

			regards, tom lane