[clang] [clang] Do not share ownership of `HeaderSearchOptions` (PR #132984)

[Ben Langmuir via cfe-commits]

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@@ -48,7 +48,7 @@ void ASTMergeAction::ExecuteAction() {
                                     /*ShouldOwnClient=*/true));
     std::unique_ptr<ASTUnit> Unit = ASTUnit::LoadFromASTFile(
         ASTFiles[I], CI.getPCHContainerReader(), ASTUnit::LoadEverything, Diags,
-        CI.getFileSystemOpts(), CI.getHeaderSearchOptsPtr());
+        CI.getFileSystemOpts(), CI.getHeaderSearchOpts());
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benlangmuir wrote:

@adrian-prantl I think this change would mean that `LoadFromASTFile` would no longer modify the header search options on `CI` here.  I'm not familiar with the ASTMerge code; do you know if that is okay?

https://github.com/llvm/llvm-project/pull/132984