Is there an example somewhere on how to link without libc and make my own syscalls? I tried this a while ago (can't remember which version of macOS it was), fiddling with Csu, nasm etc. but couldn't quite figure it out.
That's a bit annoying, especially since you're already using raw syscall numbers anyways. Here's how to make it static:
.intel_syntax noprefix
#include <sys/syscall.h>
#define UNIX_SYSCALL 0x2000000
.globl start
start:
mov rax, UNIX_SYSCALL | SYS_write
mov rdi, 1
lea rsi, text[rip]
lea rdx, length
syscall
mov rax, UNIX_SYSCALL | SYS_exit
xor rdi, rdi
syscall
text:
.asciz "Hello, world!\n"
.equ length, . - text
ld -arch x86_64 -o hello hello.o -macosx_version_min 10.8 -static -e _main