[clang] [clang] Optimize Lexer hot path to reduce compile time (PR #177153)

[Corentin Jabot via cfe-commits]

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@@ -878,6 +878,17 @@ bool Preprocessor::HandleIdentifier(Token &Identifier) {
   if (II.isExtensionToken() && !DisableMacroExpansion)
     Diag(Identifier, diag::ext_token_used);
 
+  // Handle module contextual keyword.
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cor3ntin wrote:

```suggestion
  // Handle module contextual keywords.
```

https://github.com/llvm/llvm-project/pull/177153