[clang] [clang] Implement constexpr support for __builtin_popcountg (PR #84318)

[via cfe-commits]

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@@ -157,6 +157,9 @@ Non-comprehensive list of changes in this release
 - ``__builtin_addc``, ``__builtin_subc``, and the other sizes of those
   builtins are now constexpr and may be used in constant expressions.
 
+- Added ``__builtin_popcountg`` as a type-generic alternative to
+  ``__builtin_popcount{,l,ll}`` with support for any unsigned integer type.
----------------
Sirraide wrote:

```suggestion
- ``__builtin_popcountg``, a type-generic alternative to
  ``__builtin_popcount{,l,ll}`` with support for any unsigned integer type, is
  now constexpr and may be used in constant expressions.
```

https://github.com/llvm/llvm-project/pull/84318