[clang-tools-extra] [include-cleaner] Make sure exports of stdlib also works for physical files (PR #72246)

[kadir çetinkaya via cfe-commits]

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@@ -232,6 +232,17 @@ class PragmaIncludes::RecordPragma : public PPCallbacks, public CommentHandler {
   void checkForExport(FileID IncludingFile, int HashLine,
                       std::optional<Header> IncludedHeader,
                       OptionalFileEntryRef IncludedFile) {
+    auto AddExport = [&] {
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kadircet wrote:

this was preparation for a follow-up change, but I guess it's better to do it there.

https://github.com/llvm/llvm-project/pull/72246