Fixes and improvements for Windows builds

[ndabas]

Fixes #6084. I tested the resulting output with MSVC, MSYS2 MinGW GCC, and MSYS2 CLARNGARM64 Clang.

In addition, I made some changes to the Windows ARM64 workflow:

• LLVM is installed to a new location. The path where it was being installed already had an existing copy of LLVM, so potentially we might have some files left over from the previous copy after the installation that we run.
• CMake and Ninja already exist in the runner image so removed those install steps.
• Added vswhere to lookup the actual Visual Studio install path, so future updates will not break the workflow.

[ndabas]

I've noticed some issues in the Azure pipelines as well -- I'll push fixes for those too.