Permitting non-Apple builds by not requiring IOKit

[pfarner]

Linux builds fail because the AppleSensors addon is requiring that IOKit is present:

{code}
% ./build.sh
-- Configuration set to: DebugFast
CMake Error at addons/AppleSensors/CMakeLists.txt:28 (message):
IOKit not found

-- Configuring incomplete, errors occurred!
See also "/home/presto/software/io/build/CMakeFiles/CMakeOutput.log".
See also "/home/presto/software/io/build/CMakeFiles/CMakeError.log".
-- Configuration set to: DebugFast
CMake Error at addons/AppleSensors/CMakeLists.txt:28 (message):
IOKit not found

-- Configuring incomplete, errors occurred!
See also "/home/presto/software/io/build/CMakeFiles/CMakeOutput.log".
See also "/home/presto/software/io/build/CMakeFiles/CMakeError.log".
make: *** [cmake_check_build_system] Error 1
{code}

It appears that just making the definition of that module conditional on the presence of IOKit would allow builds to succeed on non-Apple operating systems. If any other variations are desired (somehow checking the OS directly, and then requiring IOKit if on MacOS?), that could be a good modification.

[mkroehnert]

Hi, a better fix would be to only replace

    message(FATAL_ERROR "IOKit not found")
endif()

with

    message(STATUS "Not building AppleSensors because IOKit was not found")
elseif()

This would tell you in any case that the AppleSensors addon does not get built.

[mkroehnert]

Updates to existing posts don't get published via email, so please take a look at the update on the web.
I changed the previous reply so it doesn't sound (unintentionally) unfriendly.

[stevedekorte]

Thanks for the fix, Preston.
Manfred, I'd be happy to merge your change too.

[mkroehnert]

@stevedekorte my suggestion would revert the merged patch and apply what I wrote in the comment.
However, I would not like to undo the work of this pull request.
@pfarner would you like to submit a followup patch?

[pfarner]

Per mkroehnert's suggestion, I've filed another PR: #297