ravpower-mcu: 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>

package/utils/ravpower-mcu/Makefile

@@ -23,7 +23,9 @@ endef
 define Build/Compile
 	$(MAKE) -C $(PKG_BUILD_DIR) \
 		CC="$(TARGET_CC)" \
-		CFLAGS="$(TARGET_CFLAGS) -Wall"
+		CFLAGS="$(TARGET_CFLAGS) -Wall" \
+		CPPFLAGS="$(TARGET_CPPFLAGS)" \
+		LDFLAGS="$(TARGET_LDFLAGS)"
 endef
 
 define Package/ravpower-mcu/install

package/utils/ravpower-mcu/patches/001-fix-compile-flags.patch

@@ -0,0 +1,11 @@
+--- a/src/Makefile
++++ b/src/Makefile
+@@ -3,7 +3,7 @@ CFLAGS:=-I.
+ OUTDIR:=./
+ 
+ main: main.c
+-	$(CC) -o $(OUTDIR)/ravpower-mcu main.c
++	$(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) -o $(OUTDIR)/ravpower-mcu main.c
+ 
+ clean:
+ 	rm ravpower-pmic