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

[Corentin Jabot 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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cor3ntin wrote:

See my comment below. we are gonna parse that once per TU

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