[libcxx-commits] [libcxx] [libc++] Create a `constexpr` hash to use during constant evaluation (PR #214946)

[Vinay Deshmukh via libcxx-commits]

vinay-deshmukh wrote:

```
 D:/a/llvm-project/llvm-project/libcxx/test/support\constexpr_hash.h:83:11: note: non-constexpr function 'isnan<float>' cannot be used in a constant expression
```

Windows clang doesn't have constexpr std::isnan, even though stage1,2 clang does?

https://github.com/llvm/llvm-project/pull/214946