[clang] [CIR] Fix reference alignment to use pointee type (PR #186667)

[Henrich Lauko via cfe-commits]

xlauko wrote:

For example given first test case:
```
void Struct::arg_attr(Struct s, int &i, Incomplete &j){}
```

OGCG alignment is: `this = 4, s = 8, i = 4, j = 1`

CIR before this change generated:  `this = 4, s is passedby value (no alignment),  i = 8, j = 8`
CIR after this change generated: `this = 4, s is passedby value (no alignment),  i = 4, j = 1`

https://github.com/llvm/llvm-project/pull/186667