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

We need to do this now that we are bumping the minor release number when
we create the release branch.

This also results in a slight change to the library names for LLVM. The
main library now has a more convential library name:
'libLLVM.so.$major.$minor'. The old library name: libLLVM-$major.so is
now a symlink that points to the new library. However, the symlink is
not present in the build directory. It is only present in the install
directory.

The library name was changed because it helped to keep the CMake changes
more simple.

Fixes #76273

(cherry picked from commit 91a38462)