[llvm] [Support] Add Arm NEON implementation for `llvm::xxh3_64bits` (PR #99634)

[Fangrui Song via llvm-commits]

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@@ -47,6 +47,19 @@
 
 #include <stdlib.h>
 
+#if !defined(LLVM_XXH_USE_NEON)
+#if (defined(__aarch64__) || defined(_M_ARM64) || defined(_M_ARM64EC)) &&      \
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MaskRay wrote:

`clang --target=aarch64-windows-msvc -dM -xc /dev/null -E ` also defines `__aarch64__`, so the Windows specific macros might not be useful?

https://github.com/llvm/llvm-project/pull/99634