forgot another important dir for old toolchains

mk/build.mk

@@ -182,6 +182,7 @@ ${STAGING_TARGET_DIR} ${STAGING_TARGET_DIR}/etc ${STAGING_HOST_DIR}:
 	mkdir -p ${STAGING_TARGET_DIR}/bin
 	mkdir -p ${STAGING_TARGET_DIR}/etc
 	mkdir -p ${STAGING_TARGET_DIR}/usr/bin
+	mkdir -p ${STAGING_TARGET_DIR}/usr/include
 	mkdir -p ${STAGING_TARGET_DIR}/usr/lib/pkgconfig
 	mkdir -p ${STAGING_HOST_DIR}/usr/bin
 	mkdir -p ${STAGING_HOST_DIR}/usr/lib