Windows exe

[helly25]

For V19+:

• add win32.exe, win64.exe and woa.exe distributions.
• find win32.exe and woa64.exe distributions automatically.

The exe files are self extracting installers, not msiexe. However, we can extract them with a separate tool, say 7z.

[fmeum]

The change looks good, but is toolchains_llvm set up to do anything with an .exe? I've never used LLVM on Windows, but isn't that an installer?

[helly25]

The change looks good, but is toolchains_llvm set up to do anything with an .exe? I've never used LLVM on Windows, but isn't that an installer?

I'm still at my mac/linux machines and will have to figure out how I can actually teach the toolchain to work with them. Unfortunately Bazel does not use a tool for such SFX files and the toolchains will need to add support in the download implementation.

At the moment our _windows functions will return either LLVM-{llvm_version}-win32.exe or LLVM-{llvm_version}-win64.exe which is incorrect and wrong in several ways. The PR in its current form at least is a step forward.

But I'll need to work upstairs later with a windows machine to see how I can get it actually working.