parse additional system include directories from target compile flags

CMake/cotire.cmake

@@ -515,12 +515,31 @@ function (cotire_get_target_include_directories _config _language _target _inclu
 		list (APPEND _includeDirs "${CMAKE_CURRENT_BINARY_DIR}")
 		list (APPEND _includeDirs "${CMAKE_CURRENT_SOURCE_DIR}")
 	endif()
-	# parse additional include directories from target compile flags
 	set (_targetFlags "")
 	cotire_get_target_compile_flags("${_config}" "${_language}" "${_target}" _targetFlags)
-	cotire_filter_compile_flags("${_language}" "I" _dirs _ignore ${_targetFlags})
-	if (_dirs)
-		list (APPEND _includeDirs ${_dirs})
+	# parse additional include directories from target compile flags
+	if (CMAKE_INCLUDE_FLAG_${_language})
+		string (STRIP "${CMAKE_INCLUDE_FLAG_${_language}}" _includeFlag)
+		string (REGEX REPLACE "^[-/]+" "" _includeFlag "${_includeFlag}")
+		if (_includeFlag)
+			set (_dirs "")
+			cotire_filter_compile_flags("${_language}" "${_includeFlag}" _dirs _ignore ${_targetFlags})
+			if (_dirs)
+				list (APPEND _includeDirs ${_dirs})
+			endif()
+		endif()
+	endif()
+	# parse additional system include directories from target compile flags
+	if (CMAKE_INCLUDE_SYSTEM_FLAG_${_language})
+		string (STRIP "${CMAKE_INCLUDE_SYSTEM_FLAG_${_language}}" _includeFlag)
+		string (REGEX REPLACE "^[-/]+" "" _includeFlag "${_includeFlag}")
+		if (_includeFlag)
+			set (_dirs "")
+			cotire_filter_compile_flags("${_language}" "${_includeFlag}" _dirs _ignore ${_targetFlags})
+			if (_dirs)
+				list (APPEND _systemIncludeDirs ${_dirs})
+			endif()
+		endif()
 	endif()
 	# target include directories
 	get_directory_property(_dirs DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}" INCLUDE_DIRECTORIES)