[CMake] Fix installation of llvm-ranlib on multiconfig builder.

Introduce install_symlink.cmake from clang/tools/driver/clang_symlink.cmake.

FIXME: Would it be generalized?

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223655 91177308-0d34-0410-b5e6-96231b3b80d8