simplify handling target’s language standard properties

CMake/cotire.cmake

@@ -455,16 +455,17 @@ function (cotire_get_target_compile_flags _config _language _target _flagsVar)
 		if (_target)
 			get_target_property(_targetLanguageStandard ${_target} ${_language}_STANDARD)
 			if (_targetLanguageStandard)
-				get_target_property(_targetLanguageExtensions ${_target} ${_language}_EXTENSIONS)
-				if (_targetLanguageExtensions)
-					if (CMAKE_${_language}${_targetLanguageStandard}_EXTENSION_COMPILE_OPTION)
-						list (APPEND _compileFlags "${CMAKE_${_language}${_targetLanguageStandard}_EXTENSION_COMPILE_OPTION}")
-					endif()
-				else()
-					if (CMAKE_${_language}${_targetLanguageStandard}_STANDARD_COMPILE_OPTION)
-						list (APPEND _compileFlags "${CMAKE_${_language}${_targetLanguageStandard}_STANDARD_COMPILE_OPTION}")
+				set (_type "EXTENSION")
+				get_property(_isSet TARGET ${_target} PROPERTY ${_language}_EXTENSIONS SET)
+				if (_isSet)
+					get_target_property(_targetUseLanguageExtensions ${_target} ${_language}_EXTENSIONS)
+					if (NOT _targetUseLanguageExtensions)
+						set (_type "STANDARD")
 					endif()
 				endif()
+				if (CMAKE_${_language}${_targetLanguageStandard}_${_type}_COMPILE_OPTION)
+					list (APPEND _compileFlags "${CMAKE_${_language}${_targetLanguageStandard}_${_type}_COMPILE_OPTION}")
+				endif()
 			endif()
 		endif()
 	endif()