ClangTools: Fix showing diagnostics outside the project root dir

Accept diagnostics from files that are known to the project
(Project::files()) instead of checking whether they are below the
project root directory (Project::projectDirectory()).

Fixes: QTCREATORBUG-22213
Change-Id: I2f96374d6de3f53b1bd42be875dfe44b25a55fb1
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/clangtools/clangtoolslogfilereader.h

@@ -35,7 +35,7 @@ namespace ClangTools {
 namespace Internal {
 
 QList<Diagnostic> readSerializedDiagnostics(const QString &filePath,
-                                            const Utils::FilePath &projectRootDir,
+                                            const QSet<Utils::FilePath> &projectFiles,
                                             const QString &logFilePath,
                                             QString *errorMessage);