[clang] [Clang] Support libstdc++ workarounds when using `-E` (PR #210802)

[Aaron Ballman via cfe-commits]

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@@ -2978,6 +2979,10 @@ class Preprocessor {
   // Pragmas.
   void HandlePragmaDirective(PragmaIntroducer Introducer);
 
+  // Cached identifiers used to implement __set_pp_state.
+  IdentifierInfo *Ident__set_pp_state;
+  IdentifierInfo *Ident__GLIBCXX__;
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AaronBallman wrote:

True, we're not going to parse it often, but I don't see what the problem is with following the usual pattern of comparing `IdentifierInfo *`, either. I don't insist one way or the other.

https://github.com/llvm/llvm-project/pull/210802