If I WITH_SLATEC is set to 0 in perldl.conf, the PDL::Slatec will not be built and installed. That's good. However another modules like PDL::Fit::Linfit which depends on PDL::Slatec will be installed. Those modules are completely unusable in that case and they should not be installed either.
Attached patch fixes this issue in case of disabling Slatec support explicitly. However it does not help in case of disable by autodetection (WITH_SLATEC=>undef) because the autodetection is run after generating Makefiles for affected reverse dependencies.