fix bug with handling CXX_STANDARD_REQUIRED

CMake/cotire.cmake

@@ -450,20 +450,16 @@ function (cotire_get_target_compile_flags _config _language _target _flagsVar)
 		endforeach()
 	endif()
 	# handle language standard properties
-	if (_target)
-		get_target_property(_targetLanguageStandard ${_target} ${_language}_STANDARD)
-		get_target_property(_targetLanguageExtensions ${_target} ${_language}_EXTENSIONS)
-		get_target_property(_targetLanguageStandardRequired ${_target} ${_language}_STANDARD_REQUIRED)
-		if (_targetLanguageExtensions)
-			if (CMAKE_${_language}${_targetLanguageExtensions}_EXTENSION_COMPILE_OPTION)
-				list (APPEND _compileFlags "${CMAKE_${_language}${_targetLanguageExtensions}_EXTENSION_COMPILE_OPTION}")
-			endif()
-		elseif (_targetLanguageStandard)
-			if (_targetLanguageStandardRequired)
-				if (CMAKE_${_language}${_targetLanguageStandard}_STANDARD_COMPILE_OPTION)
-					list (APPEND _compileFlags "${CMAKE_${_language}${_targetLanguageStandard}_STANDARD_COMPILE_OPTION}")
+	if (CMAKE_${_language}_STANDARD_DEFAULT)
+		# used compiler supports language standard levels
+		if (_target)
+			get_target_property(_targetLanguageStandard ${_target} ${_language}_STANDARD)
+			get_target_property(_targetLanguageExtensions ${_target} ${_language}_EXTENSIONS)
+			if (_targetLanguageExtensions)
+				if (CMAKE_${_language}${_targetLanguageExtensions}_EXTENSION_COMPILE_OPTION)
+					list (APPEND _compileFlags "${CMAKE_${_language}${_targetLanguageExtensions}_EXTENSION_COMPILE_OPTION}")
 				endif()
-			else()
+			elseif (_targetLanguageStandard)
 				if (CMAKE_${_language}${_targetLanguageStandard}_EXTENSION_COMPILE_OPTION)
 					list (APPEND _compileFlags "${CMAKE_${_language}${_targetLanguageStandard}_EXTENSION_COMPILE_OPTION}")
 				endif()