Merge branch 'backport-autogen-nested-lists-fix' into release-3.10

Merge-request: !1606

Source/cmQtAutoGen.cxx

@@ -248,7 +248,7 @@ static bool RccListInputsQt5(std::string const& rccCommand,
 
 // - Class definitions
 
-std::string const cmQtAutoGen::listSep = "@LSEP@";
+std::string const cmQtAutoGen::listSep = "<<<S>>>";
 
 std::string const& cmQtAutoGen::GeneratorName(Generator type)
 {

Source/cmQtAutoGenerators.cxx

@@ -171,6 +171,9 @@ bool cmQtAutoGenerators::Run(std::string const& targetDirectory,
   snapshot.GetDirectory().SetCurrentSource(targetDirectory);
 
   auto makefile = cm::make_unique<cmMakefile>(&gg, snapshot);
+  // The OLD/WARN behavior for policy CMP0053 caused a speed regression.
+  // https://gitlab.kitware.com/cmake/cmake/issues/17570
+  makefile->SetPolicyVersion("3.9");
   gg.SetCurrentMakefile(makefile.get());
 
   bool success = false;