tst_QMutex: produce less noise with MSVC

Since MSVC doesn't have <chrono> (according to QT_HAS_INCLUDE), the QSKIP
in the test was printed for every line in the table. Instead, add the
skip in the _data() function.

Change-Id: I6e9274c1e7444ad48c81fffd14dbcee5e5a322aa
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

tests/auto/corelib/thread/qmutex/tst_qmutex.cpp

@@ -99,6 +99,9 @@ void tst_QMutex::convertToMilliseconds_data()
     QTest::addColumn<qint64>("intValue");
     QTest::addColumn<qint64>("expected");
 
+#if !QT_HAS_INCLUDE(<chrono>)
+    QSKIP("This test requires <chrono>");
+#endif
 
     auto add = [](TimeUnit unit, double d, long long i, qint64 expected) {
         const QScopedArrayPointer<char> enumName(QTest::toString(unit));