Log Message:
x11/qwt6-qt5: Fix two minor build problems

Use bsdtar, to avoid installing pax droppings and failing the PLIST check.

Skip the shlib check on a plugin, on the theory that the plugin
expects the missing library to already have been loaded, and this
appears to be the case when used in qgis.  Should perhaps be addressed
upstream, if someone really understands what is going on.