ちゃんと記事読んだら違ってたなC99ならこれだ
https://godbolt.org/z/T1Pdnj5Yb
$ gcc -x c -std=c90 -Wpedantic - <<EOF
int main() {
for (int i = 0; i < 10; ++i);
return 0;
}
EOF
<stdin>: In function ‘main’:
<stdin>:2:5: error: ‘for’ loop initial declarations are only allowed in C99 or C11 mode
<stdin>:2:5: note: use option ‘-std=c99’, ‘-std=gnu99’, ‘-std=c11’ or ‘-std=gnu11’ to compile your code
$