Merge topic 'FindPkgConfig-system-cflags'

252c66c697 FindPkgConfig: Tolerate PKG_CONFIG_SYSTEM_INCLUDE_PATH in environment
4507883135 Tests: Rename RunCMake.FindPkgConfig LIBRARY_PATH case to SYSTEM_PATH

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Merge-request: !8768