VS: Add internal API for detecting "managed" projects

This is in preparation for adding CSharp language support to the VS
generator.

Source/cmVisualStudioGeneratorOptions.cxx

@@ -137,6 +137,11 @@ bool cmVisualStudioGeneratorOptions::IsWinRt() const
   return this->FlagMap.find("CompileAsWinRT") != this->FlagMap.end();
 }
 
+bool cmVisualStudioGeneratorOptions::IsManaged() const
+{
+  return this->FlagMap.find("CompileAsManaged") != this->FlagMap.end();
+}
+
 bool cmVisualStudioGeneratorOptions::UsingUnicode() const
 {
   // Look for the a _UNICODE definition.

Source/cmVisualStudioGeneratorOptions.h

@@ -49,6 +49,7 @@ public:
 
   bool IsDebug() const;
   bool IsWinRt() const;
+  bool IsManaged() const;
   // Write options to output.
   void OutputPreprocessorDefinitions(std::ostream& fout, const char* prefix,
                                      const char* suffix,