[llvm] [CostModel][X86] getShuffleCost - shuffles with only one defined element are always cheap (PR #124412)

[Justin Bogner via llvm-commits]

bogner wrote:

Seeing a warning on the comparison between `Mask.size()` and the result of `count_if` - might need to coerce some types here:
```
X86TargetTransformInfo.cpp:1583:47: error: comparison of integers of different signs: 'size_t' (aka 'unsigned long') and 'typename iterator_traits<const int *>::difference_type' (aka 'long') [-Werror,-Wsign-compare]
```

https://github.com/llvm/llvm-project/pull/124412