[llvm] [clang] [clang][DependencyScanner] Remove unused -ivfsoverlay files (PR #73734)

[Michael Spencer via cfe-commits]

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@@ -142,6 +142,21 @@ std::vector<bool> HeaderSearch::computeUserEntryUsage() const {
   return UserEntryUsage;
 }
 
+std::vector<bool> HeaderSearch::computeVFSUsage() const {
+  std::vector<bool> VFSUsage;
+  llvm::vfs::FileSystem &RootFS = FileMgr.getVirtualFileSystem();
+  // TODO: This only works if the `RedirectingFileSystem`s were all created by
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Bigcheese wrote:

We could set a bit, and then just skip over VFSs without the bit. That would work even if people manually pass in a VFS with an extra `RedirectingFileSystem`, and we have a check later that would fire if `createVFSFromOverlayFiles ` wasn't used at all.

https://github.com/llvm/llvm-project/pull/73734