Exclude PCLBlockFilterTest when building w/o PCL
Exclude PCLBlockFilterTest when building w/o PCL

This patch puts filters/PCLBlockFilterTest.cpp inside a WITH_PCL check,
so we build with it only when we have PCL available.

DougFirErickson/PDAL,mtCarto/PDAL,radiantbluetechnologies/PDAL,lucadelu/PDAL,lucadelu/PDAL,mtCarto/PDAL,boundlessgeo/PDAL,radiantbluetechnologies/PDAL,radiantbluetechnologies/PDAL,boundlessgeo/PDAL,jwomeara/PDAL,mtCarto/PDAL,DougFirErickson/PDAL,lucadelu/PDAL,mpgerlek/PDAL-old,boundlessgeo/PDAL,jwomeara/PDAL,radiantbluetechnologies/PDAL,mpgerlek/PDAL-old,jwomeara/PDAL,DougFirErickson/PDAL,Sciumo/PDAL,DougFirErickson/PDAL,mpgerlek/PDAL-old,Sciumo/PDAL,mpgerlek/PDAL-old,Sciumo/PDAL,lucadelu/PDAL,mtCarto/PDAL,Sciumo/PDAL,jwomeara/PDAL,boundlessgeo/PDAL