Handle belowNormalPriority inside process launcher on Windows

Remove setCreateProcessArgumentModifier() from the ProcessInterface
API and replace it with belowNormalPriority flag.

Change-Id: I6bcb92e56c3a68af7fa3e3a1c8b8eb13e3a2e5a7
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/processutils.cpp

@@ -26,6 +26,13 @@
 #include "processutils.h"
 #include <QProcess>
 
+#ifdef Q_OS_WIN
+#ifdef QTCREATOR_PCH_H
+#define CALLBACK WINAPI
+#endif
+#include <qt_windows.h>
+#endif
+
 namespace Utils {
 
 QIODevice::OpenMode ProcessStartHandler::openMode() const
@@ -55,4 +62,16 @@ void ProcessStartHandler::handleProcessStarted(QProcess *process)
     }
 }
 
+
+void ProcessStartHandler::setBelowNormalPriority(QProcess *process)
+{
+#ifdef Q_OS_WIN
+    process->setCreateProcessArgumentsModifier(
+        [](QProcess::CreateProcessArguments *args) {
+            args->flags |= BELOW_NORMAL_PRIORITY_CLASS;
+    });
+#endif // Q_OS_WIN
+}
+
+
 } // namespace Utils