cmake: fixed os.cmake to work when conan install is already run
cmake: fixed os.cmake to work when conan install is already run

AnnikaH/IncludeOS,mnordsletten/IncludeOS,AnnikaH/IncludeOS,hioa-cs/IncludeOS,mnordsletten/IncludeOS,mnordsletten/IncludeOS,alfred-bratterud/IncludeOS,AndreasAakesson/IncludeOS,hioa-cs/IncludeOS,hioa-cs/IncludeOS,hioa-cs/IncludeOS,mnordsletten/IncludeOS,AndreasAakesson/IncludeOS,AndreasAakesson/IncludeOS,alfred-bratterud/IncludeOS,mnordsletten/IncludeOS,AnnikaH/IncludeOS,alfred-bratterud/IncludeOS,mnordsletten/IncludeOS,AndreasAakesson/IncludeOS,alfred-bratterud/IncludeOS,AndreasAakesson/IncludeOS,AndreasAakesson/IncludeOS,AnnikaH/IncludeOS,AnnikaH/IncludeOS,alfred-bratterud/IncludeOS,hioa-cs/IncludeOS