CMake 向下相容性 CXX

定義一堆向後相容性變數

CMAKE_ANSI_CXXFLAGS - flag for ansi c++
CMAKE_HAS_ANSI_STRING_STREAM - has <strstream>
include(TestForANSIStreamHeaders)
include(CheckIncludeFileCXX)
include(TestForSTDNamespace)
include(TestForANSIForScope)