-Werror,-Wunused-but-set-variable

Change-Id: I4e4d3c810e9d37fd4b87d3307c2ba906923aa63b
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/165882
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <stephan.bergmann@allotropia.de>

compilerplugins/clang/unusedmember.cxx

@@ -126,6 +126,8 @@ public:
                 {
 #if 0 //TODO: friend function definitions are not marked as referenced even if used?
                     if (!d3->isThisDeclarationADefinition()) //TODO: do this check for all kinds?
+#else
+                    (void)d3;
 #endif
                     {
                         continue;