Merge topic 'ci-clang15-windows'

46b2849550 ci: Update LLVM/Clang to 15.0 in nightly CI jobs on Windows
3eb94e4d51 ci: Simplify LLVM/Clang CI job specs on Windows
8ba5835c8d ci: Factor out helper to load clang into environment on Windows
bf2e4a2e85 ci: Factor out helper to load ninja into environment on Windows
93ff726114 Tests: Fix TryCompile bad source case for clang-cl 15 on Windows

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !7897