No valid executable file was produced by the compiler /nix/store/js66s0xwjnzg0ggi2lq9bcvlk6x2za13-binutils-2.35.2/bin/ld: /nix/store/z56jcx3j1gfyk4sv7g8iaan0ssbdkhz1-glibc-2.33-56/lib/crt1.o: in function _start': /build/glibc-2.33/csu/../sysdeps/x86_64/start.S:104: undefined reference to main' collect2: 错误：ld 返回 1 什么意思