Merge topic 'modules-better-messages'

571b5e1f cxxmodules: improve error messages for C++ module setup
8b4d32c1 cmStandardLevelResolver: add query for the effective standard level
17ddc4ac cmStandardLevelResolver: compare with static string literals
6f1dae2b cmStandardLevelResolver: use `cmStrCat` where possible
0d45d40e cmStandardLevelResolver: use character literals where possible

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Merge-request: !8755