[clang] [coroutine] Suppress unreachable-code warning on coroutine statements. (PR #77454)

[Utkarsh Saxena via cfe-commits]

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@@ -493,26 +454,68 @@ bool DeadCodeScan::isDeadCodeRoot(const clang::CFGBlock *Block) {
   return isDeadRoot;
 }
 
-static bool isValidDeadStmt(const Stmt *S) {
+// Check if the given `DeadStmt` is a coroutine statement and is a substmt of
+// the coroutine statement.
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usx95 wrote:

Could you also describe the second param CFGBlock ? 
eg. `Block` is the CFGBlock containing the `DeadStmt`.

https://github.com/llvm/llvm-project/pull/77454