[clang] [lldb] Serialize `#pragma redefine_extname` into precompiled headers. (PR #186755)

[Chuanqi Xu via cfe-commits]

================
@@ -6061,6 +6059,22 @@ ASTFileSignature ASTWriter::WriteASTCore(Sema *SemaPtr, StringRef isysroot,
     }
   }
 
+  // Write the set of #pragma redefine_extname'd, undeclared identifiers. We
+  // always write the entire table, since later PCH files in a PCH chain are
+  // only interested in the results at the end of the chain.
+  RecordData ExtnameUndeclaredIdentifiers;
+  if (SemaPtr) {
----------------
ChuanqiXu9 wrote:

But generally we won't propagate preprocessor detectives. I do feel this is not good to leak it. This is inconsistent the  design of named modules for isolation. 

https://github.com/llvm/llvm-project/pull/186755