[clang] [clang][PAC] Add __builtin_get_vtable_pointer (PR #139790)

[Oliver Hunt via cfe-commits]

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@@ -3074,6 +3074,39 @@ following way:
 
 Query for this feature with ``__has_builtin(__builtin_offsetof)``.
 
+``__builtin_get_vtable_pointer``
+--------------------------------
+
+``__builtin_get_vtable_pointer`` loads and authenticates the primary vtable
+pointer from an instance of a polymorphic C++ class.
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ojhunt wrote:

Basic docs have been and I've added a reference

https://github.com/llvm/llvm-project/pull/139790