Add QDebug streaming operator for ProString

This saves us lots of .toQString() and .toQStringList() typing when
qDebug()'ing qmake code.

Change-Id: I037e5e1816f2dcb6a20dec4c275f3d886f155ad5
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

qmake/library/proitems.cpp

@@ -517,4 +517,9 @@ ProKey ProFile::getHashStr(const ushort *&tPtr)
     return ret;
 }
 
+QDebug operator<<(QDebug debug, const ProString &str)
+{
+    return debug << str.toQString();
+}
+
 QT_END_NAMESPACE

qmake/library/proitems.h

@@ -31,6 +31,7 @@
 
 #include "qmake_global.h"
 
+#include <qdebug.h>
 #include <qstring.h>
 #include <qvector.h>
 #include <qhash.h>
@@ -468,6 +469,8 @@ struct ProFunctionDefs {
     QHash<ProKey, ProFunctionDef> replaceFunctions;
 };
 
+QDebug operator<<(QDebug debug, const ProString &str);
+
 QT_END_NAMESPACE
 
 #endif // PROITEMS_H