QMake: fix GCC 9 -Wdeprecated-copy warnings

Not visible in QMake, because of too old C++ standard used to compile it,
but in the qttools copy. Fix here, as the authorative source, first.

Change-Id: I2552eccfaab2cef0863686dcd888f2a5f25ca29f
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

1 files changed, 1 insertions, 0 deletions

diff --git a/qmake/library/proitems.h b/qmake/library/proitems.h
index cc65421556..ff7c8b92f7 100644
--- a/qmake/library/proitems.h
+++ b/qmake/library/proitems.h
@@ -68,6 +68,7 @@ class ProString {
 public:
     ProString();
     ProString(const ProString &other);
+    ProString &operator=(const ProString &) = default;
     PROITEM_EXPLICIT ProString(const QString &str);
     PROITEM_EXPLICIT ProString(const QStringRef &str);
     PROITEM_EXPLICIT ProString(const char *str);