Fix unused variable suppression on Windows

MSVC fails with undefined type error when an argument passed by
reference but suppressed as normal variable.

Change-Id: I93a89aea4fae5f820c9ab0d1222d63b01ca3ed3c
Reviewed-by: Michael Bruning <michael.bruning@digia.com>
Reviewed-by: Andras Becsi <andras.becsi@digia.com>