If you like that, there is yet another seldom seen feature of c99, the use of '' in an array declarator:
echo 'int my_func(int i, int arr[*]);' > main.c
gcc -c -std=c99 main.c
-- * observe that there are no errors * --
Edit: I can't figure out how to escapse an asterisk, so the above might not read correctly but I tried.