Autogen: Add cmQtAutogenGlobalInitializer::Keywords class

The new `cmQtAutogenGlobalInitializer::Keywords` class instance is bound to
the lifetime of the `cmQtAutogenGlobalInitializer` instance.  Global static
const strings would be allocated at program start and deallocated at program
end.  Keeping keyword strings alive only in the context where they're
needed helps to reduce the memory footprint.

Source/cmQtAutoGenGlobalInitializer.cxx

@@ -20,6 +20,13 @@
 #include <memory>
 #include <utility>
 
+cmQtAutoGenGlobalInitializer::Keywords::Keywords()
+  : AUTOMOC("AUTOMOC")
+  , AUTOUIC("AUTOUIC")
+  , AUTORCC("AUTORCC")
+{
+}
+
 cmQtAutoGenGlobalInitializer::cmQtAutoGenGlobalInitializer(
   std::vector<cmLocalGenerator*> const& localGenerators)
 {

Source/cmQtAutoGenGlobalInitializer.h

@@ -17,11 +17,25 @@ class cmQtAutoGenInitializer;
 /// @brief Initializes the QtAutoGen generators
 class cmQtAutoGenGlobalInitializer
 {
+public:
+  /// @brief Collection of QtAutogen related keywords
+  class Keywords
+  {
+  public:
+    Keywords();
+
+    std::string AUTOMOC;
+    std::string AUTOUIC;
+    std::string AUTORCC;
+  };
+
 public:
   cmQtAutoGenGlobalInitializer(
     std::vector<cmLocalGenerator*> const& localGenerators);
   ~cmQtAutoGenGlobalInitializer();
 
+  Keywords const* kw() const { return Keywords_.get(); };
+
   bool generate();
 
 private:
@@ -48,6 +62,7 @@ private:
   std::map<cmLocalGenerator*, std::string> GlobalAutoGenTargets_;
   std::map<cmLocalGenerator*, std::string> GlobalAutoRccTargets_;
   std::unordered_map<std::string, std::string> ExecutableTestOutputs_;
+  std::unique_ptr<Keywords> Keywords_;
 };
 
 #endif