Fix broken creation of the debug symbols

debian/rules

@@ -1,5 +1,7 @@
 #!/usr/bin/make -f
 
+export CFLAGS:=$(shell dpkg-buildflags --get CFLAGS)
+
 ifeq ($(SOURCE_DATE_EPOCH),)
     # workaround until SOURCE_DATE_EPOCH is available
     $(info SOURCE_DATE_EPOCH is not set, using changelog date instead)