Fix size of struct with POD pointer in it

[spencer-lunarg]

closes #293

Will now print

struct Data{
   int a;
   int* b;
   int c;
};
[[vk::push_constant]] Data pc;

as

  Push constant blocks: 1

    0:
      spirv id : 16
      name     : pc (Data_std140)
          // size = 20, padded size = 20
          struct Data_std140 {
              int  a; // abs offset =  0, rel offset =  0, size = 4, padded size = 4 UNUSED
              int* b; // abs offset =  8, rel offset =  8, size = 8, padded size = 8 UNUSED
              int  c; // abs offset = 16, rel offset = 16, size = 4, padded size = 4
          } pc;