QtSupport: Readd PROPARSER_THREAD_SAFE for qbs build

Removed by mistake on 618115c3



Change-Id: Ia87cef28f312a4c951bdac6d366d8b0feb7f1737
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>

src/plugins/qtsupport/qtsupport.qbs

@@ -26,6 +26,7 @@ QtcPlugin {
             "QT_NO_CAST_TO_ASCII",
             "QMAKE_AS_LIBRARY",
             "QMAKE_LIBRARY",
+            "PROPARSER_THREAD_SAFE",
             "PROEVALUATOR_THREAD_SAFE",
             "PROEVALUATOR_CUMULATIVE",
             "QMAKE_BUILTIN_PRFS"