Build LLVM for Windows

[athei]

This PR changes the CI build scripts to also build LLVM for windows. It doesn't build revive itself for windows. This will come in a follow up. But once we have a LLVM binary release the turn around time will be much quicker for experimenting with the revive windows build.

I manually uploaded the release those changes produce here. This enables this PR's CI to find the proper release. This is necessary because I am also making changes to the folder structure and artifact naming that the other CI jobs are depending on.

Releases generated from this branch can be inspected here: https://github.com/paritytech/revive-alex-workflowtest/releases/tag/v0.1.0-dev.12

Summary of changes:

• Change llvm-builder to use MSVC toolchain on windows
• Fix llvm-builder to work with .exe files
• Unify the llvm release jobs into a single one. This removed a lot of copy pasted code and also speeds up the build by giving each their own runner.
• Use the LLVM target triple to name the binary releases instead of an ad-hoc naming convention
• Remove the nested folder hierarchy inside the llvm release. Its just now a single folder llvm-<target> that contains the toolchain.
• Give jobs and workflows consistent names
• Replace all runners bei their *-latest counterpart
• Only use parity-large to build llvm now. All other jobs use github runners

[xermicus]

Nice