Fixes#1054.
Previously, bit-fields followed by another field were aligned
to two bytes. Bit-fields ending the struct were (and continue
to be) aligned only to a single byte.
```
struct s {
unsigned int x : 4;
};
struct t {
unsigned int x : 4;
unsigned int y;
};
```
Before: `sizeof(struct s) == 1`, sizeof(struct t) == 4`
After: `sizeof(struct s) == 1` sizeof(struct t) == 3`
9858e47dfd