...
PKG_BUILD_DEPENDS:=libubox
CMAKE_INSTALL:=1
include $(INCLUDE_DIR)/package.mk
include $(INCLUDE_DIR)/cmake.mk
TARGET_CFLAGS += -Wno-error=enum-int-mismatch
CMAKE_OPTIONS += -DLWS_IPV6=$(if $(CONFIG_IPV6),ON,OFF)
CMAKE_OPTIONS += -DISABLE_WERROR=ON
CMAKE_OPTIONS += -DCMAKE_BUILD_TYPE=Release
CMAKE_OPTIONS += -DLWS_WITH_EXTERNAL_POLL=ON
CMAKE_OPTIONS += -DLWS_WITH_ULOOP=ON
...
but adding
TARGET_CFLAGS += -Wno-error=enum-int-mismatchto Makefile allows building..