avutil/tests: improved code coverage for atomic

Signed-off-by: Thomas Turner <thomastdt@googlemail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/tests/atomic.c

@@ -22,6 +22,8 @@
 int main(void)
 {
     volatile int val      = 1;
+    void *tmp1            = (int *)&val;
+    void * volatile *tmp2 = &tmp1;
     int res;
 
     res = avpriv_atomic_int_add_and_fetch(&val, 1);
@@ -29,6 +31,8 @@ int main(void)
     avpriv_atomic_int_set(&val, 3);
     res = avpriv_atomic_int_get(&val);
     av_assert0(res == 3);
+    avpriv_atomic_ptr_cas(tmp2, tmp1, &res);
+    av_assert0(*tmp2 == &res);
 
     return 0;
 }