Adding missing -std=c99 flag for files that won't compile without it

Många hade problem med de filerna och kunde inte kompilera dem. Detta commit löser problemet.

```
celsius> make fib-iter
gcc -Wall -ggdb -o fib-iter fib-iter.c
fib-iter.c: In function 'fib':
fib-iter.c:7:3: error: 'for' loop initial declarations are only allowed in C99 mode
fib-iter.c:7:3: note: use option -std=c99 or -std=gnu99 to compile your code
make: *** [fib-iter] Error 1
celsius> make fib-count
gcc -Wall -ggdb -o fib-count fib-count.c
fib-count.c: In function 'main':
fib-count.c:25:3: error: 'for' loop initial declarations are only allowed in C99 mode
fib-count.c:25:3: note: use option -std=c99 or -std=gnu99 to compile your code
fib-count.c:39:12: error: redefinition of 'i'
fib-count.c:25:12: note: previous definition of 'i' was here
fib-count.c:39:3: error: 'for' loop initial declarations are only allowed in C99 mode
make: *** [fib-count] Error 1
celsius> make fib-memo
gcc -Wall -ggdb -o fib-memo fib-memo.c
fib-memo.c: In function 'main':
fib-memo.c:29:3: error: 'for' loop initial declarations are only allowed in C99 mode
fib-memo.c:29:3: note: use option -std=c99 or -std=gnu99 to compile your code
make: *** [fib-memo] Error 1
```