[clang] [Clang] Add GCC's __builtin_stack_address() to Clang. (PR #121332)

[Aaron Ballman via cfe-commits]

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@@ -899,6 +899,12 @@ def FrameAddress : Builtin {
   let Prototype = "void*(_Constant unsigned int)";
 }
 
+def StackAddress : Builtin {
+  let Spellings = ["__builtin_stack_address"];
+  let Attributes = [NoThrow];
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AaronBallman wrote:

I wasn't 100% sure; I thought it meant two consecutive calls from the same context, but I can never remember that detail. I'm fine leaving it off though -- we can easily add it later if we find there's a benefit. Thanks!

https://github.com/llvm/llvm-project/pull/121332