[clang] [clang] Add __builtin_start_object_lifetime builtin. (PR #82776)

[Richard Smith via cfe-commits]

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@@ -896,6 +896,12 @@ def Launder : Builtin {
   let Prototype = "void*(void*)";
 }
 
+def StartObjectLifeTime : Builtin {
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zygoloid wrote:

Nit: lifetime is one word not two, so the `T` should not be capitalized.

https://github.com/llvm/llvm-project/pull/82776