Created attachment 517134 [details]
ebuild with workaround
The pcl_features-1.8.pc installed by the sci-libs/pcl-1.8.1 ebuild contains a bogus dependency on pcl_2d-1.8, a component that doesn't exist any more. The breakage obviously comes from upstream, but just removing the dependency is straightforward enough. So let's try and get this temp fix into portage, since doesn't seem to be doing a lot of maintenance releases.
*upstream [doesn't seem to be doing a lot of maintenance releases]
Speaking for 1.12.1 here, which still has the 2d in pcl_features-1.12.pc
Are you sure this is the correct solution? From my research, it's true that the pcl_2d-1.12.so file is no more. But the pkgconfig file doesn't list any libraries with the pcl_2d-1.12.pc file, just dependencies on pcl_common and pcl_filters.
The cmake configuration output states, that the subsystem 2d will be built, thus I assume, the subsystem is still available, it just doesn't give any library and is instead included in the common and filters subsystems.