popt was integrated with rpm in rpm-3.0.4, before that it was a separate package (popt-1.4 SRPM was the last one released). Now, while upgrading 5.x I came across an interesting circular dependency: rebuilding rpm-3.0.4*.src.rpm requires >= popt-1.5, which can't in turn be rebuilt, because it's now part of aforementioned rpm package! This can be avoided by grabbing a binary popt distribution off ftp.rpm.org. Still, this seems to be something to fix.
Either build with --nodeps, or simply delete the BuildPrereq:. The dependency is for the 1st popt version with a shared library, which is needed to build python bindings correctly.