[compiler-rt] [compiler-rt] Add cpu model init for Windows. (PR #111961)

[Daniel Kiss via llvm-commits]

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@@ -0,0 +1,42 @@
+#ifndef _ARM64_
+#define _ARM64_
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DanielKristofKiss wrote:

`windows.h` defines it so let's do that.

https://github.com/llvm/llvm-project/pull/111961