[clang-tools-extra] Add --project-root to clangd (PR #155905)

[Nathan Ridge via cfe-commits]

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@@ -69,14 +71,17 @@ class GlobalCompilationDatabase {
   }
 
 protected:
+  std::optional<std::string> WorkingDirectory;
   mutable CommandChanged OnCommandChanged;
 };
 
 // Helper class for implementing GlobalCompilationDatabases that wrap others.
 class DelegatingCDB : public GlobalCompilationDatabase {
 public:
-  DelegatingCDB(const GlobalCompilationDatabase *Base);
-  DelegatingCDB(std::unique_ptr<GlobalCompilationDatabase> Base);
+  DelegatingCDB(const GlobalCompilationDatabase *Base,
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HighCommander4 wrote:

Likewise here, we may want to give these added parameters a default

https://github.com/llvm/llvm-project/pull/155905