How to include both for loop initial declarations and gnu extensions?

I have this code:

#include <string.h>
#include <stdio.h>

char numbers[5] = "12345";

int main(){
  memrchr(numbers,'2',5);
  for(int i=0;i<5;i++){
    printf("%d",i);
  }
  return 0;
}

It uses for loop inital declarations (for(int i) and gnu extensions (memrchr).

I am using the compiler gcc

The problem is that it doesn't seem to let both go through. I can either do

gcc program.c -o program

Which complains about the for loops, or I can do

gcc -std=gnu11 program.c -o program

Which complains about memrchr being undefined. (or rather it complains about the implicit declaration of the function)

How do I do both? Is it possible?