contrib: qt: allow building in debug mode

contrib/src/qt/rules.mak

@@ -102,7 +102,11 @@ QT_CONFIG := -static -opensource -confirm-license $(QT_OPENGL) -no-pkg-config \
 	-no-compile-examples -nomake examples -nomake tests \
 	-system-freetype -system-harfbuzz -system-libjpeg -system-libpng -system-zlib
 
+ifdef WITH_OPTIMIZATION
 QT_CONFIG += -release
+else
+QT_CONFIG += -debug
+endif
 
 ifeq ($(V),1)
 QT_CONFIG += -verbose