Fix plugin install libdir.

CalamaresAddLibrary.cmake

@@ -89,23 +89,29 @@ function(calamares_add_library)
 
     if(NOT LIBRARY_INSTALL_BINDIR)
         set(LIBRARY_INSTALL_BINDIR "${CMAKE_INSTALL_BINDIR}")
+        set(LIBRARY_INSTALL_LIBDIR "${CMAKE_INSTALL_LIBDIR}")
+    else()
+        set(LIBRARY_INSTALL_LIBDIR "${LIBRARY_INSTALL_BINDIR}")
     endif()
 
+    message("INSTALL_BINDIR: ${LIBRARY_INSTALL_BINDIR}")
+    message("INSTALL_LIBDIR: ${LIBRARY_INSTALL_LIBDIR}")
+
     # make installation optional, maybe useful for dummy plugins one day
     if(NOT LIBRARY_NO_INSTALL)
         include(GNUInstallDirs)
         if(NOT LIBRARY_EXPORT)
             install( TARGETS ${target}
                 RUNTIME DESTINATION ${LIBRARY_INSTALL_BINDIR}
-                LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
-                ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+                LIBRARY DESTINATION ${LIBRARY_INSTALL_LIBDIR}
+                ARCHIVE DESTINATION ${LIBRARY_INSTALL_LIBDIR}
             )
         else()
             install( TARGETS ${target}
                 EXPORT ${LIBRARY_EXPORT}
                 RUNTIME DESTINATION ${LIBRARY_INSTALL_BINDIR}
-                LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
-                ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+                LIBRARY DESTINATION ${LIBRARY_INSTALL_LIBDIR}
+                ARCHIVE DESTINATION ${LIBRARY_INSTALL_LIBDIR}
             )
         endif()
     endif()