Switch to building libqrencode with CMake. Note that upstream (https://github.com/fukuchi/libqrencode) hasn’t seen any activity for ~4 years, so the odds of getting anything upstream seems low, but I’ve made two minor changes to the source here, which I will PR in any case.
From an initial look I couldn’t find any significant difference between the Autotools and CMake produced libs. As part of this change we move cmake-minimal in Guix into the global package set.