crude dprintf() shim for Illumos and Haiku OS

dprintf.c

int dprintf(int fd, const char *restrict format, ...) {
    va_list ap;
    FILE *f = fdopen(fd, "w");

    if (!f) {
        return -1;
    }

    va_start(ap, format);
    int result = fprintf(f, format, ap);
    va_end(ap);

    return result;
}