Merge topic 'CheckPIESUpported-supports-SYSROOT'

219dde4ea8 CheckPIESupported: now uses any SYSROOT settings
4fa105d34e Check{Compiler,Linker}Flag: Add possibility to retrieve check outputs

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Merge-request: !6877