[clang] [Clang] Introduce __builtin_is_modifiable_lvalue() (PR #132524)

[Timm Baeder via cfe-commits]

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@@ -964,6 +964,13 @@ def IsConstantEvaluated : LangBuiltin<"CXX_LANG"> {
   let Prototype = "bool()";
 }
 
+def IsLValue : Builtin {
+  let Spellings = ["__builtin_is_modifiable_lvalue"];
+  let Attributes = [NoThrow, CustomTypeChecking, UnevaluatedArguments,
+                    Constexpr];
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tbaederr wrote:

There is no constexpr implementation in this patch.

https://github.com/llvm/llvm-project/pull/132524