CMake: fix version comparison

[nim65s]

Hi again,

On CentOS 7, with CMake 3.7.2, I get the following issue:

CMake Error at cmake/compilerOptions.cmake:93 (include):
include could not find load file:

CheckLinkerFlag
Call Stack (most recent call first):
CMakeLists.txt:30 (include)

CMake Error at cmake/compilerOptions.cmake:94 (check_linker_flag):
Unknown CMake command "check_linker_flag".
Call Stack (most recent call first):
CMakeLists.txt:30 (include)

[tbeu]

Thanks for reporting and fixing.