Type cast to function pointer doesn't work

[ForNeVeR]

See a comment in Cesium.IntegrationTests/type_casts.c (introduced in #377):

    // function pointer types are not supported yet?
    // int j = (int) (void (*)(int a)) a;
    // int k = (int) (void (*)(int a)) (a + b);
    // if (j + k != 5) return -5;

We should investigate this problem.