Fix trigger of infinite recursion in MSVC when converting a path to a string

src/dds/compdb.cpp

     for (const compile_file_plan& cf : iter_compilations(plan)) {
         auto command = cf.generate_compile_command(env);
         auto entry   = nlohmann::json::object({
-            {"directory", env.output_root},
+            {"directory", env.output_root.string()},
             {"arguments", command},
             {"file", cf.source_path().string()},
         });