ClangCodeModel: Fix build with Qt 5.15

Artificially lower the number of function parameters in
generateCompilationDB(), to accommodate Qt5's QtConcurrent::run().

Change-Id: Ide88925deb443378b9308d924406ec6f6f90e8aa
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/clangcodemodel/clangmodelmanagersupport.cpp

@@ -424,7 +424,8 @@ void ClangModelManagerSupport::updateLanguageClient(
     const ClangDiagnosticConfig warningsConfig = warningsConfigForProject(project);
     auto future = Utils::runAsync(&Internal::generateCompilationDB, projectInfo, jsonDbDir,
                                   CompilationDbPurpose::CodeModel,
-                                  warningsConfig, optionsForProject(project, warningsConfig),
+                                  qMakePair(warningsConfig,
+                                            optionsForProject(project, warningsConfig)),
                                   includeDir);
     generatorWatcher->setFuture(future);
     m_generatorSynchronizer.addFuture(future);