Settings::ExternalBuilder::systems make set

Nothing cares about the order, actually.

Author: Ericson2314

src/libstore/include/nix/store/globals.hh

@@ -1375,7 +1375,7 @@ public:
 
     struct ExternalBuilder
     {
-        std::vector<std::string> systems;
+        StringSet systems;
         Path program;
         std::vector<std::string> args;
     };

src/libstore/unix/build/external-derivation-builder.cc

@@ -19,10 +19,9 @@ struct ExternalDerivationBuilder : DerivationBuilderImpl
         LocalStore & store, std::unique_ptr<DerivationBuilderCallbacks> & miscMethods, DerivationBuilderParams & params)
     {
         for (auto & handler : settings.externalBuilders.get()) {
-            for (auto & system : handler.systems)
-                if (params.drv.platform == system)
-                    return std::make_unique<ExternalDerivationBuilder>(
-                        store, std::move(miscMethods), std::move(params), handler);
+            if (handler.systems.contains(params.drv.platform))
+                return std::make_unique<ExternalDerivationBuilder>(
+                    store, std::move(miscMethods), std::move(params), handler);
         }
         return {};
     }