[spirv][amdgpu] Set atomic size in the clang target info (#128569)

Problem identified by Joseph. The openmp device runtime uses
__scoped_atomic_load_n and similar which presently hit

```
error: large atomic operation may incur significant performance
      penalty; the access size (4 bytes) exceeds the max lock-free size (0 bytes) [-Werror,-Watomic-alignment]
```

This is because the spirv class doesn't set the corresponding field. The
base does, but only if there's a host toolchain, which there isn't.

0 files changed, 0 insertions, 0 deletions