[llvm] [ADT] Simplify hash_combine (NFC) (PR #159938)

[Jakub Kuderski via llvm-commits]

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@@ -483,8 +483,11 @@ namespace detail {
 /// recursive combining of arguments used in hash_combine. It is particularly
 /// useful at minimizing the code in the recursive calls to ease the pain
 /// caused by a lack of variadic functions.
-struct hash_combine_recursive_helper {
+struct hash_combine_helper {
   char buffer[64] = {};
+  char *buffer_ptr;
+  char *const buffer_end;
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kuhar wrote:

do we need this? Isn't it always the end of `buffer`?

https://github.com/llvm/llvm-project/pull/159938