Valgrind: Fix test build

Amends 25b1c59f74.

Change-Id: Ibbc2ab6aca74e8bffa97bca53909daf2240a3eab
Reviewed-by: hjk <hjk@qt.io>

src/plugins/valgrind/valgrindrunner.cpp

@@ -281,6 +281,11 @@ void ValgrindRunner::waitForFinished() const
     loop.exec();
 }
 
+QString ValgrindRunner::errorString() const
+{
+    return d->m_valgrindProcess.errorString();
+}
+
 bool ValgrindRunner::start()
 {
     return d->run();

src/plugins/valgrind/valgrindrunner.h

@@ -56,6 +56,8 @@ public:
 
     void waitForFinished() const;
 
+    QString errorString() const;
+
     bool start();
     void stop();