when resolving symbols with only weak defs, use first def, not last def

[musl] / src / process / posix_spawnattr_getpgroup.c

#include <spawn.h>

int posix_spawnattr_getpgroup(const posix_spawnattr_t *attr, pid_t *pgrp)
{
        *pgrp = attr->__pgrp;
        return 0;
}