What kind of warning is this?
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined
/home/openwrt/master/openwrt/staging_dir/toolchain-x86_64_gcc-9.3.0_musl/include/stddef.h:7: warning: "NULL" redefined