debugger: rename 'magic' prefix for custom dumper from qqDump to qdump__

It is nicer in the presence of namespaces as '::' will be replaced by '__'
to create the dumper function names.

tests/auto/debugger/tst_gdb.cpp

@@ -3616,6 +3616,7 @@ void breaker() {}
 
 int main(int argc, char *argv[])
 {
+    char *x = argv[0];
     #ifdef QT_GUI_LIB
     QApplication app(argc, argv);
     #else