Merge topic 'cmPolicies-cmStrCat'

c4bb7fd4f3 cmPolicies: use `cmStrCat` for error message building
59eda7fa0a cmPolicies: use `cmStrCat` for string additions
0c8a2c4a86 cmPolicies: use character literals where possible
0cb4f08ddf cmPolicies: combine string literals where possible

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Merge-request: !8650