go like defer in c, but only works with gcc or clang

• gcc support is done via gcc nested function, when compiling, you might need to add -z execstack to have a executable stack.
• clang support is done via clang blocks, when compiling, you need to add -fblocks and for some platform, -lBlocksRuntime.

#include <stdio.h>
#include <stdlib.h>
#include "defer.h"

int main( void )
{
    int* arr = malloc(sizeof (int) * 10);
    defer(free(arr));
    defer({
        printf("world\n");
    });
    printf("Hello ");
    return 0;
}