Drop the static LLVM libraries on Windows MSVC CI

[HertzDevil]

Supersedes #15074. This should now be completely doable after #15765.

[HertzDevil]

For convenience, LLVM_TARGETS now accepts commas, used to pass string arrays in PowerShell, and semicolons, used when building LLVM with CMake, as additional separators, on top of the whitespace, used by llvm-config.exe. It is highly unlikely any valid LLVM target name would contain a comma or semicolon.