ci: Update LLVM/Clang to 15.0 in nightly CI jobs on Windows (!7897) · Merge requests · CMake / CMake

Also factor out helpers for loading Ninja and Clang into the environment, and use them to simplify the job specs.

Backport: release

Edited Nov 10, 2022 by Brad King

ci: Update LLVM/Clang to 15.0 in nightly CI jobs on Windows