cmGeneratorTarget: add HasLanguage() as wrapper for GetLanguages()

Source/cmGeneratorTarget.cxx

@@ -5195,6 +5195,18 @@ void cmGeneratorTarget::GetLanguages(std::set<std::string>& languages,
   }
 }
 
+bool cmGeneratorTarget::HasLanguage(std::string const& language,
+                                    std::string const& config,
+                                    bool exclusive) const
+{
+  std::set<std::string> languages;
+  this->GetLanguages(languages, config);
+  // add linker language (if it is different from compiler languages)
+  languages.insert(this->GetLinkerLanguage(config));
+  return (languages.size() == 1 || !exclusive) &&
+    languages.count(language) > 0;
+}
+
 void cmGeneratorTarget::ComputeLinkImplementationLanguages(
   const std::string& config, cmOptionalLinkImplementation& impl) const
 {

Source/cmGeneratorTarget.h

@@ -364,6 +364,12 @@ public:
   void GetLanguages(std::set<std::string>& languages,
                     std::string const& config) const;
 
+  // Evaluate if the target uses the given language for compilation
+  // and/or linking. If 'exclusive' is true, 'language' is expected
+  // to be the only language used for the target.
+  bool HasLanguage(std::string const& language, std::string const& config,
+                   bool exclusive = true) const;
+
   void GetObjectLibrariesCMP0026(
     std::vector<cmGeneratorTarget*>& objlibs) const;