[clang] [clang-tools-extra] Reland [clang][Sema, Lex, Parse] Preprocessor embed in C and C++ (PR #95802)

[Eli Friedman via cfe-commits]

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@@ -2422,6 +2422,10 @@ void ExprEngine::Visit(const Stmt *S, ExplodedNode *Pred,
       Bldr.addNodes(Dst);
       break;
     }
+
+    case Stmt::EmbedExprClass:
+      llvm_unreachable("Support for EmbedExpr is not implemented.");
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efriedma-quic wrote:

Please don't use llvm_unreachable for things which are actually reachable.  At the very least, use report_fatal_error.  Prefer a real diagnostic when possible.

https://github.com/llvm/llvm-project/pull/95802