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

[Nathan Ridge via cfe-commits]

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@@ -117,6 +122,12 @@ class DirectoryBasedGlobalCompilationDatabase
     // Only look for a compilation database in this one fixed directory.
     // FIXME: fold this into config/context mechanism.
     std::optional<Path> CompileCommandsDir;
+    // Working directory for fallback commands
+    // If unset, parent directory of file should be used
+    std::optional<std::string> WorkingDirectory;
+
+    void
+    applyWorkingDirectory(const std::optional<std::string> &&WorkingDirectory);
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HighCommander4 wrote:

What is the purpose of using `const &&` here?

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