define FIX =
ifdef $(1)
CFLAGS += '-D$(1)="$$($(1))"'
CPPFLAGS += '-D$(1)="$$($(1))"'
#$$(info USING $(1)=$$($(1)))
endif
endef

$(eval $(call FIX,WIFI_SSID))
$(eval $(call FIX,WIFI_PASSWORD))
$(eval $(call FIX,MQTT_HOST))
$(eval $(call FIX,MQTT_PORT))

fix: