[compiler-rt] [compiler-rt] Add initial ARM64EC builtins support (PR #139279)

[Jacek Caban via llvm-commits]

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@@ -10,9 +10,22 @@ extern void __enable_execute_stack(void* addr);
 
 typedef int (*pfunc)(void);
 
+#ifdef __x86_64__
+// On ARM64EC, we need the x86_64 version of this function, but the compiler
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cjacek wrote:

I changed this to use `__arm64ec__`.

https://github.com/llvm/llvm-project/pull/139279