BUG: apply patch from Qt upstream for gcc 9

SuperBuild/patches/QT5/qt5-5-gcc9-mersenne_twister-all.diff

+--- a/qtbase/src/corelib/global/qrandom.cpp
++++ b/qtbase/src/corelib/global/qrandom.cpp
+@@ -218,6 +218,7 @@ struct QRandomGenerator::SystemGenerator
+ #endif // Q_OS_WINRT
+ 
+     static SystemGenerator &self();
++    typedef quint32 result_type;
+     void generate(quint32 *begin, quint32 *end) Q_DECL_NOEXCEPT_EXPR(FillBufferNoexcept);
+ 
+     // For std::mersenne_twister_engine implementations that use something
+-- 
+2.16.3
+