[CMake] Add compatibility and current versioning to libLTO to match autoconf support.

This also adds LLVM_LTO_VERSION_OFFSET to support functional equivalence to autoconf.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@250245 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed