[clang] [clang] Change representation of CurLexerKind (PR #70381)

[via cfe-commits]

================
@@ -751,13 +751,8 @@ class Preprocessor {
   std::unique_ptr<TokenLexer> CurTokenLexer;
 
   /// The kind of lexer we're currently working with.
-  enum CurLexerKind {
-    CLK_Lexer,
-    CLK_TokenLexer,
-    CLK_CachingLexer,
-    CLK_DependencyDirectivesLexer,
-    CLK_LexAfterModuleImport
-  } CurLexerKind = CLK_Lexer;
+  typedef bool (*CurLexerKindType)(Preprocessor &, Token &);
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cor3ntin wrote:

```suggestion
  typedef bool (*LexerCallback)(Preprocessor &, Token &);
```

https://github.com/llvm/llvm-project/pull/70381