Yeah, so the syntax is a bit funny but you can actually get the bounds checking you want here:

  #include <stdio.h>

  static void qux(int a[static 6]){
    printf("%d\n", a[8]);
  }

  int main() {
    int a[5] = {1, 2, 3, 4, 5};
    qux(a);
  }

I get,

  test.c:9:5: warning: array argument is too small; contains 5 elements, callee requires at least 6 [-Warray-bounds]

I did not enable any warning flags at all, this is just default Clang on a Mac.

If you want to catch the a[8] inside the function you need something else.