Allow INIT_FLAVOR override in makefile fragment

makefile

 
 build/Makefile: CMakeLists.txt
 	mkdir -p build
-	cd build && cmake .. -DCMAKE_BUILD_TYPE=Release
+	cd build && cmake .. -DCMAKE_BUILD_TYPE=Release $(addprefix -DINIT_FLAVOR=,$(INIT_FLAVOR))
 
-