D26752: ECMAddAppIcon: Do not warn about mac icons if isnt a mac build

[patrick j pereira]

patrickelectric added reviewers: apol, tcanabrava.

REPOSITORY
  R240 Extra CMake Modules

REVISION DETAIL
  https://phabricator.kde.org/D26752

To: patrickelectric, apol, tcanabrava
Cc: kde-frameworks-devel, kde-buildsystem, LeGast00n, GB_2, bencreasy, 
michaelh, ngraham, bruns