binutils: 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 <[email protected]>

package/devel/binutils/Makefile

@@ -93,6 +93,9 @@ CONFIGURE_ARGS += \
 	--without-msgpack \
 	--disable-gprofng
 
+MAKE_VARS+= \
+	CPPFLAGS="$(TARGET_CPPFLAGS)"
+
 define Build/Install
 	$(call Build/Install/Default)
 	$(MAKE) -C $(PKG_BUILD_DIR)/libiberty \