Merge topic 'platform-vars' a136b6ec98 MINGW: Define variable only when targeting Windows platforms 39c5dad0cb Ninja: Remove redundant check for GNU-like compiler on Windows 0b7ae84a96 Cygwin: Remove redundant definitions of CYGWIN and UNIX variables Acked-by: Kitware Robot <kwrobot@kitware.com> Acked-by: buildbot <buildbot@kitware.com> Merge-request: !6538