Update CMakeLists.txt
Update CMakeLists.txt

set gcc compiler variable CMAKE_C_COMPILER and CMAKE_CXX_COMPILER before checking gcc's version
morningman/palo,imay/palo,cyongli/palo,morningman/palo,morningman/palo,morningman/palo,lingbin/palo,cyongli/palo,lingbin/palo,lingbin/palo,cyongli/palo,lingbin/palo,cyongli/palo,imay/palo,imay/palo,imay/palo,lingbin/palo,imay/palo,imay/palo,lingbin/palo,morningman/palo,cyongli/palo,cyongli/palo,morningman/palo