[llvm] [llvm-shlib] Fix the version naming style of libLLVM for Windows (PR #85710)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> If its like with v17 it should be good I think

Yep, I checked, and e.g. `llvm-config --libs mc` prints `-lLLVM-19git` right now, which is the right thing for the mingw target.

For the unix targets, it should still work as we do provide `libLLVM-19git.so` as a symlink to `libLLVM.so.19.0git`. If we change it to return `-lLLVM` instead, please only do that change for unix targets, as the mingw/windows one still should keep using the `-lLLVM-19git` form.

https://github.com/llvm/llvm-project/pull/85710