camke中判断操作系统平台有两种方法：
1.
MESSAGE(STATUS "operation system is ${CMAKE_SYSTEM}")
IF (CMAKE_SYSTEM_NAME MATCHES "Linux")
MESSAGE(STATUS "current platform: Linux ")
ELSEIF (CMAKE_SYSTEM_NAME MATCHES "Windows")
MESSAGE(STATUS "current platform: Windows")
ELSEIF (CMAKE_SYSTEM_NAME MATCHES "FreeBSD")
MESSAGE(STATUS "current platform: FreeBSD")
ELSE ()
MESSAGE(STATUS "other platform: ${CMAKE_SYSTEM_NAME}")
ENDIF (CMAKE_SYSTEM_NAME MATCHES "Linux")
MESSAGE(STSTUS "###################################")2.
IF (WIN32)
MESSAGE(STATUS "Now is windows")
ELSEIF (APPLE)
MESSAGE(STATUS "Now is Apple systens.")
ELSEIF (UNIX)
MESSAGE(STATUS "Now is UNIX-like OS's.")
ENDIF ()