COMP: Ensure custom qt style plugins are fixed-up on MacOSX

This is a follow-up of commit r22238 ensuring the style plugins
are considered as candidate by the fixup script.

See #3253

Signed-off-by: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22684 3bd1e089-480b-0410-8dfb-8563597acbee