More containsPreprocessingConditionalInclusion checking in loplugin:casttovoid

...to avoid false positive with --disable-dbgutil in SfxApplication ctor
(sfx2/source/appl/app.cxx), which contains

    bool bOk = InitializeDde();
  #ifdef DBG_UTIL
    ...
  #else
    (void)bOk;
  #endif

Change-Id: I4de6322a848a9c6aea3057e4598b2161888dee6a
Reviewed-on: https://gerrit.libreoffice.org/53051Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

compilerplugins/clang/casttovoid.cxx

@@ -380,6 +380,11 @@ private:
                 } else if (!i.second.castToVoid.empty()
                            && !isWarnUnusedType(i.first->getType()))
                 {
+                    auto const fun = dyn_cast_or_null<FunctionDecl>(i.first->getDeclContext());
+                    assert(fun != nullptr);
+                    if (containsPreprocessingConditionalInclusion(fun->getSourceRange())) {
+                        continue;
+                    }
                     report(
                         DiagnosticsEngine::Warning,
                         "unused variable %select{declaration|name}0",