I am able to compile the following using gcc version 4.7.2

```
   #include <string.h>

   int main(){
    char text[] = "String duplicate";
    char* dup = strdup(text);
    return 0;

   }

```

But when I used the --std=c11 flag, I get the following warning:

```
warning: implicit declaration of function ‘strdup’ [-Wimplicit-function-declaration]
warning: initialization makes pointer from integer without a cast [enabled by default]

```

What changed to cause this warning?