[clang] [llvm] [clang][deps] Overload `Filesystem::exists` in `DependencyScanningFilesystem` to have it use cached `status` (PR #88152)

[Jan Svoboda via cfe-commits]

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@@ -270,6 +270,12 @@ DependencyScanningWorkerFilesystem::status(const Twine &Path) {
   return Result->getStatus();
 }
 
+bool
+DependencyScanningWorkerFilesystem::exists(const Twine &Path) {
+  llvm::ErrorOr<llvm::vfs::Status> Status = status(Path);
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jansvoboda11 wrote:

Would be good to explain why it's necessary & okay to kill the `exists()` optimization here.

https://github.com/llvm/llvm-project/pull/88152