Merge topic 'fix-cxx20-detection'

5e7c8f44ac Ninja: Restore support for compilers not defining a C++ standard level

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Acked-by: Jaeden Amero <kitware@patater.com>
Acked-by: Martin Kojtal <martin.kojtal@arm.com>
Merge-request: !7896