6rd: add CPPFLAGS

Forward the OpenWrt CPPFLAGS to the compile process. This fixes fortify
sources support.

Link: https://github.com/openwrt/openwrt/pull/22056
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit b497c3f68f)

package/network/ipv6/6rd/Makefile

@@ -35,6 +35,7 @@ define Build/Compile
 	$(MAKE) -C $(PKG_BUILD_DIR) \
 		CC="$(TARGET_CC)" \
 		CFLAGS="$(TARGET_CFLAGS) -Wall" \
+		CPPFLAGS="$(TARGET_CPPFLAGS)" \
 		LDFLAGS="$(TARGET_LDFLAGS)"
 endef
 

package/network/ipv6/6rd/src/Makefile

@@ -1,7 +1,7 @@
 all: 6rdcalc
 
 6rdcalc: 6rdcalc.c
-	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $<
+	$(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) -o $@ $<
 
 clean:
 	rm -f 6rdcalc