[llvm] [cmake] Add minor version to library SONAME (PR #79376)

[Khem Raj via llvm-commits]

kraj wrote:

its creating symlink `libLLVM-<major-ver>.so` pointing to `libLLVM.so` I think it would be nicer for packagers if it was pointing to newly renamed `libLLVM.so.maj.minor`

https://github.com/llvm/llvm-project/pull/79376