[clang] [Clang] use constant evaluation context for constexpr if conditions (PR #123667)

[Erich Keane via cfe-commits]

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@@ -2203,6 +2203,12 @@ Parser::ParseCXXCondition(StmtResult *InitStmt, SourceLocation Loc,
       return ParseCXXCondition(nullptr, Loc, CK, MissingOK);
     }
 
+    EnterExpressionEvaluationContext Eval(
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erichkeane wrote:

This doesn't quite seem right to me, as it is covering parsing at least 2 things, do we really intend that? 

https://github.com/llvm/llvm-project/pull/123667