test.c

/* 
env MACOSX_DEPLOYMENT_TARGET=10.7 clang -o test10.7 test.c
objdump -s test10.7
env MACOSX_DEPLOYMENT_TARGET=12.0 clang -o test12.0 test.c
objdump -s test12.0
clang -o testunspec test.c
# note the replacement 
objdump -s testunspec
# note the replacement of __DATA,__mod_init_func with __TEXT,__init_offsets
*/

#include <stdio.h>

void myinit(int argc, char **argv, char **envp) {
        printf("%s: %s\n", __FILE__, __FUNCTION__);
}
__attribute__((section("__DATA,__mod_init_func"))) typeof(myinit) *__init = myinit;

int main(int argc, char **argv, char **envp) {
        /* the below __init doesn't link on macOS 12.0, with no deployment target env var set:
         * ld: reference to symbol (which has not been assigned an address) ___init in '_main'
         */
        __init(argc, argv, envp);
        printf("%s: %s\n", __FILE__, __FUNCTION__);
        return 0;
}